radicals - uni-kiel.de · 3 + studied by vacuum ultraviolet synchrotron radiation 12.00 – 13.30...

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32nd International Symposium

on Free Radicals

Book of Abstracts

Potsdam 2013 Germany

32nd International Symposium

on Free Radicals

Potsdam, Germany, 21–26 July 2013 www.freeradicals2013.de

International Board

Chair

T. A. Miller (Columbus)

E. Bieske (Melbourne)

A. Carrington (Southampton)

P. Casavecchia (Perugia)

R. Colin (Brussels)

R. F. Curl (Houston)

L. Halonen (Helsinki)

E. Hirota (Yokohama)

W. E. Jones (Halifax)

S. Kable (Sydney)

Secretary

R. Continetti (San Diego)

M. Larsson (Stockholm)

S. Leach (Paris)

Y-P. Lee (Taipei)

J. P. Maier (Basel)

A. J. Merer (Taipei)

J. J. ter Meulen (Nijmegen)

T. C. Steimle (Tempe)

I. Tanaka (Tokyo)

B. A. Thrush (Cambridge, UK)

Local Organizing Committee

Peter Botschwina (Chair)

Georg-August-University Göttingen

[email protected]

Friedrich Temps (Chair)

Christian-Albrechts-University Kiel

[email protected]

Gernot Friedrichs (Co-Chair) Christian-Albrechts-University Kiel

Hans-Gerd Löhmannsröben (Co-Chair) University of Potsdam

Tanja Sharif (Conference Secretary) Christian-Albrechts-University Kiel

Ole Hüter (Web Master) Christian-Albrechts-University, Kiel

Table of Contents

General Information

Conference History i

Support / Sponsors ii

Information iii

Surrounding Area Map iv

Programme 1

Abstracts

Invited Lectures & Hot Topic Talks 7

Poster Session A 43

Poster Session B 93

Index 141

i

History of the International Symposium on Free Radicals

The biannual International Symposium on Free Radicals series aims to provide a strongly interdisciplinary forum for chemists, physicists, astrophysicists and environmental scientists for exchanging the latest research results on diverse aspects, experiment and theory, of free radicals. This international meeting dates back to 1956, when it was first held in Quebec City, Canada, and since then has been successfully continued at conference venues in North America, Europe, Asia, and Australia.

Year Location Symposium Chair(s) 1956 Quebec City, CANADA P. A. Giguere

1957 Washington DC, USA H. P. Broida, A. M. Bass

1958 Sheffield, UK G. Porter

1959 Washington DC, USA H. P. Broida, A. M. Bass

1961 Uppsala, SWEDEN S. Claesson

1963 Cambridge, UK B. A. Thrush

1965 Padua, ITALY G. Semerano

1967 Novosibirsk, USSR V. N. Kondratiev

1969 Banff, CANADA H. Gunning, D. A. Ramsay

1971 Lyon, FRANCE M. Peyron

1973 Königssee, GERMANY W. Groth

1976 Laguna Beach, CA, USA E. K. C. Lee, F. S. Rowland

1977 Lyndhurst, Hants, UK A. Carrington

1979 Sanda, Hyogo-ken, JAPAN Y. Morino, I. Tanaka

1981 Ingonish, NS, CANADA W. E. Jones

1983 Lauzelles-Ottignies, BELGIUM R. Colin

1985 Granby, CO, USA K. M. Evenson, R. F. Curl, H. E. Radford

1987 Oxford, UK J. M. Brown

1989 Dalian, CHINA Postponed

1990 Susono, Shizuoka, JAPAN H. Hirota

1991 Williamstown, MA, USA S. D. Colson

1993 Doorworth, NETHERLANDS H. ter Meulen

1995 Victoria, BC, CANADA A. J. Merer

1997 Tallberg, SWEDEN M. Larsson

1999 Flagstaff, AZ, USA T. A. Miller

2001 Assisi, ITALY P. Casavecchia

2004 Taipei, TAIWAN Y. P. Lee

2005 Leysin, SWITZERLAND J. P. Maier, F. Merkt, M. Quack

2007 Big Sky, MT, USA R. E. Continetti

2009 Savonlinna, FINLAND L. Halonen, R. Timonen

2011 Port Douglas, AUSTRALIA E. J. Bieske, S. H. Kable

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Support / Sponsors

The organizers of the 32nd International Symposium on Free Radicals gratefully acknowledge the support by the following organizations and companies.

In the framework of International Bunsen Discussion Meetings the German Bunsen Society for Physical Chemistry (DBG) aims to promote research and technical advances in the area of physical chemistry. It supports basic and applied research in pure and interdisciplinary physico-chemical research.

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Information

Lectures & Posters

Please upload your presentation to the conference laptop or use your own laptop and test your presentation or laptop in time – prior to the respective session.

Each poster presenter will be given one minute (= 60 seconds) prior to the start of the respective poster session to advertise his/her work using one slide. Please submit your one slide as email attachment to: [email protected] (PowerPoint, max. 1 MB). Pins for attaching posters are supplied.

Internet

Wireless internet is available through Seminaris SeeHotel.

Important Phone Numbers

Intern. dialing code +49 (Germany) FRS2013 Contact (0)151 50410969 (Tanja Sharif, Conference Office) Seminaris SeeHotel +49 (0)331 9090-0 Taxi-Call Potsdam +49 (0)331 292929 Emergency/Ambulance 112 Drugstore (nearest) (0)331 95130830; distance 3 km Shopping Center “Kaufland” Zeppelinstr. 132, 14471 Potsdam Hospital (nearest) (0)331 96820; distance 5 km St. Josef Krankenhaus Potsdam Allee nach Sanssouci 7, 14471 Potsdam

Recreation

Next to the amenities found at the Seminaris SeeHotel, leisure and sporting activities are easily available in the nearby surrounding (see map on next page). For manifold sightseeing highlights and cultural programs in Potsdam and Berlin please refer to the corresponding tourist information websites (www.potsdam-tourism.com/ ; www.berlin.de/en/ ; www.visitberlin.de/en) and the supplied information material in your conference bag.

Water taxi “Potsdam Wassertaxi” connects the hotel directly to downtown Potsdam and to some of the parks and palaces. It runs every 1-2 hours (3.50 – 9.00 EUR); www.potsdamer-wassertaxi.de/fahrplan.php.

Jogging/Walking Around the lake or in the “Pirschheide” (the forrested area just behind the Seminaris SeeHotel).

Bike Rental Up to 40 bikes are available through Seminaris SeeHotel, see reception desk; 6.00 EUR/2h – 16.00 EUR/24h.

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Boat Rental “Windsurfing Potsdam”; canoes, motorboats, surfing; near camping site; www.wassersport-in-potsdam.de; distance 0.5 km.

Public Beach / Boat Rental “Waldbad Templin” 3.00 EUR; rowboats, paddleboats, kayaks; take water taxi to “Forsthaus/Strandbad Templin” or use footway across railroad embankment (distance 2.5 km).

Wakeboarding “Magix Wakeboarding”; take water taxi to “Forsthaus/Strandbad Templin” or use footway across railroad embankment (distance 2.3 km); www.magix-wakeboarding.de/.

Surrounding Area Map

1

Programme

Sunday, July 21th 2013

14.00 – 18.00 Registration 18.00 – 20.00 Dinner 20.00 – 22.00 Welcome Reception Monday, July 22nd

2013 8.25 Opening / Introductory Remarks Session I Ultrafast processes in gaseous and condensed media (Chair: Terry A. Miller) 08.30 – 09.10 I-01 Hans Jacob Wörner Probing electronic structure and dynamics with high- harmonic spectroscopy 09.10 – 09.50 I-02 Peter Vöhringer Solvated electron dynamics in liquid-to-supercritical solvents 09.50 – 10.10 H-01 Petr Slavíček Novel type of ultrafast relaxation process in hydrogen- bonded systems: Implications to radiation chemistry 10.10 – 10.40 Coffee Session II Radicals at low temperature (Chair: Helmut Beckers) 10.40 – 11.20 I-03 Ian R. Sims Radical reactivity at low temperatures 11.20 – 12.00 I-04 Wolfgang E. Ernst Cluster aggregation, spin dynamics, and cold reactions in doped helium droplets 12.00 – 14.00 Lunch 14.00 – 18.00 Free time

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18.00 – 19.30 Dinner Poster Session A 19.30 – 22.30 Poster Introduction & Presentation Tuesday, July 23rd

2013 Session III Free radicals and electronically excited states at surfaces (Chair: Lauri Halonen) 08.30 – 09.10 I-05 Alec M. Wodtke Electronically nonadiabatic interactions of free radicals at metal surfaces: Does the unpaired electron matter? 09.10 – 09.50 I-06 Thorsten Klüner Ab initio surface photochemistry 09.50 – 10.10 H-02 Yuan-Pern Lee Infrared spectra of protonated pyrene and coronene and their neutral counterparts in solid para-hydrogen 10.10 – 10.40 Coffee break Session IV Radicals in bimolecular reactions (Chair: David Chandler) 10.40 – 11.20 I-07 Piergiorgio Casavecchia Reaction dynamics of oxygen atoms with unsaturated hydrocarbons: primary radical and molecular products, branching ratios and role of intersystem crossing 11.20 – 12.00 I-08 Laurie J. Butler Defying and ducking intrinsic reaction coordinates: Experiments and theory on radical intermediates 12.00 – 14.00 Lunch 14.00 – 18.00 Free time 18.00 – 19.30 Dinner Session V Radicals in the environment (Chair: Harald Berresheim) 19.30 – 20.10 I-09 Christa Fittschen HO2 radicals everywhere, but how to detect them? 20.10 – 20.50 I-10 G. Barney Ellison Climate change, biomass energy, and organic radicals

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Wednesday, July 24th 2013

Session VI Dynamics and kinetics of radicals in solution (Chair: Jürgen Troe) 08.30 – 09.10 I-11 Andrew Orr-Ewing Vibrationally resolved dynamics of free radical reactions in solution 09.10 – 09.50 I-12 Michael Buback Polymerization processes understood via the kinetics of elementary radical reactions 09.50 – 10.10 H-03 Timothy W. Schmidt Resonance stabilized radicals from H addition to aromatic rings 10.10 – 10.40 Coffee break

Session VII Anions and electron attachment to radicals (Chair: Robert E. Continetti) 10.40 – 11.20 I-13 Nick Shuman Electron attachment to fluorocarbon radicals 11.20 – 11.40 H-04 C. Romanzin/ C. Alcaraz Reactions of state-selected O+ cations and nitrile anions of interest for astrochemistry 11.40 – 12.00 H-05 Mitchio Okumura Threshold photoelectron-photoion coincidence spectroscopy of the nitrate cation NO3

+ studied by vacuum ultraviolet synchrotron radiation 12.00 – 13.30 Lunch 13.30 – 18.30 Conference Excursion by boat to Schloss Cecilienhof 18.30 – 19.30 Dinner

Poster Session B 19.30 – 22.30 Poster Introduction & Presentation

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Thursday, July 25th 2013

Session VIII New developments in theory and applications (Chair: Wolfgang Eisfeld) 08.30 – 09.10 I-14 Hans-Joachim Werner New multi-reference electronic structure methods 09.10 – 09.50 I-15 Millard H. Alexander Rotational and electronic relaxation of the CH2 radical in collisions with He 09.50 – 10.10 H-06 Jens-Uwe Grabow Rotational spectra in service of particle physics: Zeeman and hyperfine effects 10.10 – 10.40 Coffee break Session IX Photodissociation and phototautomerization (Chair: Koichi Tsukiyama) 10.40 – 11.20 I-16 Jingsong Zhang High-resolution studies of photodissociation dynamics of polyatomic free radicals 11.20 – 12.00 I-17 Scott H. Kable Radical, triplet, molecular, roaming and triple fragmentation pathways in H2CO: Quantum yields and dynamics across ~1 eV of excitation 12.00 – 14.00 Lunch Session X Crossed beam studies of radical reactions (Chair: Anthony J. Merer) 14.00 – 14.40 I-18 Xueming Yang Reagent vibrational excitation effect on the dynamics of the F + HD reaction 14.40 – 15.20 I-19 Toshinori Suzuki Crossed beam ion imaging study of O(1D) reaction with methane 15.20 – 15.50 Coffee break Session XI New developments in spectroscopy (Chair: Sidney Leach) 15.50 – 16.10 H-07 Evan J. Bieske Photoisomerization action spectroscopy of molecular ions in the gas phase

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16.10 – 16.30 H-08 Eizi Hirota A new type of vibronic interactions in the nitrate free radical NO3 16.30 – 16.50 H-09 Terry A. Miller Rotationally resolved spectra of Jahn-Teller active free radicals 18.00 – 23.00 Transfer to Sanssouci Palace and Conference Dinner at Restaurant “Historische Mühle” Friday, July 26th

2013 Session XII Radicals and ions in astrochemistry (Chair: Lucy M. Ziurys) 08.30 – 09.10 I-20 Harold Linnartz Solid state pathways towards molecular complexity in space – free radicals @ work 09.10 – 09.30 H-10 Oliver Welz Reactivity of Criegee intermediates CH2OO and CH3CHOO: direct detection and conformer-dependent kinetics 09.30 – 09.50 H-11 Gernot Friedrichs Issues of NO formation in flames via the NCN radical pathway: rate constants, absorption cross section, and thermochemistry 09.50 – 10.10 H-12 Ingo Fischer Dimerization of phenylpropargyl radicals: an IR/UV double resonance study 10.10 – 10.40 Coffee break Session XIII Free radicals in combustion (Chair: John P. Maier) 10.40 – 11.20 I-21 Tina Kasper Detection of reactive radicals in combustion chemistry 11.20 – 12.00 I-22 David L. Osborn Non-adiabatic reaction chemistry of O(3P) atoms with unsaturated hydrocarbons 12.05 – 14.00 Lunch 13.30 Departure

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-- Notes --

7

Invited Lectures

&

Hot Topic Talks

(in the order of presentation)

I-01 Invited Lecture

8

Probing Electronic Structure and Dynamics with

High-Harmonic Spectroscopy

Hans Jacob Wörner

Laboratorium für Physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Straße 10 8093 Zürich, Switzerland

The process of attosecond pulse generation in molecules offers a new fully coherent spectroscopic approach to studying electronic structure and dynamics. We will show how this technique can be used to measure the motion of electrons in the valence shell of molecules with unprecedented sensitivity. A previously unobserved inelastic pathway of high-harmonic emission amplifies a weak electronic excitation (0.1 % population) to a strong signal modulation (20 %). Working with spatially aligned and oriented molecules, the technique allows us to probe subtle structures and asymmetries in the electronic valence shell of molecules. Finally, exploiting the correlation between the continuum electron wave packet and the bound electron-hole wave packet, we are able to resolve attosecond electronic dynamics in molecules triggered by electron correlation.

Invited Lecture I-02

9

Solvated electron dynamics in liquid-to-supercritical solvents

Janus Urbanek, Joel Torres-Alacan, Stephan Kratz, Jörg Lindner, Peter Vöhringer

Institute for Physical and Theoretical Chemistry, University of Bonn,

Wegelerstraße 12, 53115 Bonn, Germany The solvated electron is the “mother of all radicals”. Formally, it constitutes an unpaired negative elementary charge embedded in a condensed-phase matrix where it is self-stabilized by polarizing its immediate vicinity. The matrix may be a solid or a liquid and it may be ordered or (statically and dynamically) disordered. In the language of solid-state physics, the electron moves together with its polarization cloud as a quasi-particle, the so-called polaron. However, because of its atomic/molecular structure, the matrix will not always be able to adiabatically follow the electronic motion. Instead, the nuclear degrees of freedom of the matrix will readjust to the moving charge in an inertial fashion such that a complex time-lag between structural matrix distortions and electronic excitations is introduced.

In the context of solvated electrons in liquids, a fundamental and heavily debated issue is the motif of electron binding to a liquid matrix. Is the solvated electron trapped in a cavity-type void created within the liquid with the surrounding molecules forming conventional solvation shell structures? Or do we have to regard the solvated electron as a solvated radical anion cluster in which the spin and charge densities are diffusely smeared out over a larger number of solvent molecules? How does the electronic binding mode affect the physico-chemical and optical properties of such solutions and is the chemical reactivity of a solvated “cavity electron” different to that of a solvated “radical cluster electron”?

To address some of these questions, we have recently carried out extensive studies on the femtosecond spectroscopy of solvated electrons in hydrogen bonded solvents like water, alcohols, and ammoniae.g. 1-5. The solvated electrons were generated chemically (e.g. in metal-ammonia solutions) or photolytically via multi-photon ionization of the neat solvent. The solvent was studied over a wide range of thermodynamic conditions ranging from the densely packed cryogenic liquid all the way over to the dilute supercritical fluid with gas-like densities. In this talk, we will describe some of the progress we have made to understand the chemical reactivity of solvated electron with a particular emphasis on the dynamics of geminate recombination following an ultrafast optical ionization with energies above and below the band gap of the solvent. Such studies will be discussed in terms of Lars Onsager’s seminal theory for the initial recombination of ions in condensed media6 and in terms of detailed Monte-Carlo computer simulations to account for the molecular-level mechanisms that bring about an annihilation of the excess charge and spin densities. Acknowledgment: Financial support by the Deutsche Forschungsgemeinschaft through the Collaborative Research Center 813 “Chemistry @ Spin Centers” is gratefully acknowledged. 1. J. Lindner, A.-N. Unterreiner, P. Vöhringer, ChemPhysChem 7, 363 (2006). 2. J. Lindner, A.-N. Unterreiner, P. Vöhringer, J. Chem. Phys. 129, 064514 (2008). 3. S. Kratz, J. Torres-Alacan, J. Urbanek, J. Lindner, P. Vöhringer, Phys. Chem. Chem. Phys. 12, 12169 (2010). 4. J. Torres-Alacan, S. Kratz, P. Vöhringer, Phys. Chem. Chem. Phys. 13, 20806 (2011). 5. J. Urbanek, A. Dahmen, J. Torres-Alacan, P. Königshoven, J. Lindner, P. Vöhringer, J. Phys. Chem. B, 116,

2223 (2012). 6. L. Onsager, Phys. Rev. 54, 554 (1938).

H-01 Hot Topic

10

Novel Type of Ultrafast Relaxation Process in Hydrogen Bonded Systems:

Implications to Radiation Chemistry

P. Slavíček,a) N. Kryzhevoi,b) B. Winter c)

a) Department of Physical Chemistry, Institute of Chemical Technology, Technická 5, 16628 Prague 6, Czech Republic and J. Heyrovský Institute of Physical Chemistry, v.v.i.,

Dolejškova 3, 18223 Prague 8, Czech Republic b) Theoretical Chemistry, Institute of Physical Chemistry, Heidelberg University,

D-69120 Heidelberg, Germany c) Helmholtz-Zentrum Berlin für Materialien und Energie, and BESSY

D-12489 Berlin, Germany The primary products formed in the first few femtoseconds upon water X-ray irradiation are so far only incompletely characterized. Upon the ejection of inner-valence or inner shell electron, the molecule loses energy via local relaxation processes such as X-ray fluorescence (leading to singly charged molecule) or Auger process (leading to doubly charged molecule). Relatively recently, non-local electronic relaxation processes such as Intermolecular Coulomb Decay (ICD) have been identified.1,2 Using a combination of liquid photoemission, quantum chemistry and quantum dynamics methods, we have identified a novel type of relaxation process specific for hydrogen bonded systems, the so called proton transfer mediated charge separation (PTM-CS).3 In the PTM-CS process, the electron autoionization is preceded by an ultrafast (less than 10 fs) proton transfer between two neighboring water units, leading to Zundell-like [HO*··H··OH2]+ structures. Ultimately, dicationic, charge separated species of the [H2O+•H2O+](aq) and [OH+•H3O+](aq) type are formed. The implications for radiation chemistry will be discussed. We will present a detailed analysis of the PTM-CS process for liquid water and for solvated hydrogen peroxide.4,5 Finally, we will also discuss the limits of the efficiency of the inner valence ICD process imposed by a nuclear dynamics. Acknowledgment: P.S. acknowledges project number 13-34168S by the Grant Agency of The Czech Republic. 1. M. Mucke, M. Braune, S. Barth, M. Forstel, T. Lischke, V. Ulrich, T. Arion, U. Becker, A. Bradshaw, U.

Hergenhahn, Nat. Phys. 6, 143 (2010). 2. T. Jahnke, H. Sann, T. Havermeier, K. Kreidi, C. Stuck, M. Meckel, M. Schoffler, N. Neumann, R.

Wallauer, S. Voss, A. Czasch, O. Jagutzki, A. Malakzadeh, F. Afaneh, Th. Weber, H. Schmidt-Bocking, R. Dorner, Nat. Phys. 6, 139 (2010).

3. S. Thürmer, N. Ottosson, R. Seidel; U. Hergenhahn; S. E. Bradforth, P. Slavíček and B. Winter, Nat. Chem. accepted for a publication.

4. S. Thürmer, I. Unger, P. Slavíček and B. Winter, J. Phys. Chem. (submitted). 5. P. Slavíček, B. Winter, L. Cederbaum, N. Kryzhevoi (in preparation).


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Radical Reactivity at Low Temperatures

Ian R. Sims

Institut de Physique de Rennes, UMR CNRS-UR1 6251, Université de Rennes 1, 263 Avenue

du Général Leclerc, 35042 Rennes Cedex, France The use of the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme, or Reaction Kinetics in Uniform Supersonic Flow) technique coupled with pulsed laser photochemical kinetics methods1 has revolutionised the field of low temperature kinetics of free radicals in the gas phase. Radical-radical, radical-unsaturated molecule and even radical-saturated molecule reactions have been shown to be rapid down to the temperatures of dense interstellar clouds (10 – 20 K), and the results have had a major impact in astrochemistry and planetology, as well as proving an exacting test for theory.2 Rate coefficients have been measured as low as 5.8 K for the reaction S(1D) + H2.3 The technique has also been applied to the formation of transient complexes of interest both in atmospheric chemistry4 and combustion.5 It is thought that long chain cyanopolyyne molecules H(C2)nCN may play an important role in the formation of the orange haze layer in Titan’s atmosphere. The longest carbon chain molecule observed in interstellar space, HC11N, is also a member of this series. I will present new results, obtained in collaboration with Jean-Claude Guillemin (Ecole de Chimie de Rennes) and Stephen Klippenstein (Argonne National Labs), on reactions of C2H, CN and C3N radicals which contribute to the low temperature formation of (cyano)polyynes. Until now, all of the chemical reactions studied in this way have taken place on attractive potential energy surfaces with no overall barrier to reaction. The F + H2 HF + H reaction does possess a substantial energetic barrier (≌ 800 K), and might therefore be expected to slow to a negligible rate at very low temperatures. It is nevertheless the only source of interstellar HF, recently detected in a wide variety of environments by the Herschel Space Observatory, many of which are very cold (10 – 100 K). In fact, this H-atom abstraction reaction does take place efficiently at low temperatures due entirely to tunneling. I will report direct experimental measurements of the rate of this reaction down to a temperature of 11 K, in remarkable agreement with state-of-the-art quantum reactive scattering calculations by François Lique (Université du Havre) and Millard Alexander (University of Maryland). 1. I. R. Sims, J. L. Queffelec, A. Defrance, C. Rebrion-Rowe, D. Travers, P. Bocherel, B. R. Rowe, I. W. M.

Smith, J. Chem. Phys. 100, 4229 (1994). 2. H. Sabbah, L. Biennier, I. R. Sims, Y. Georgievskii, S. J. Klippenstein, I. W. M. Smith, Science 317, 102

(2007). 3. C. Berteloite, M. Lara, A. Bergeat, S. D. Le Picard, F. Dayou, K. M. Hickson, A. Canosa, C. Naulin, J. M.

Launay, I. R. Sims, M. Costes, Phys. Rev. Lett. 105, 203201 (2010). 4. S. D. Le Picard, M. Tizniti, A. Canosa, I. R. Sims, I. W. M. Smith, Science 328, 1258 (2010). 5. H. Sabbah, L. Biennier, S. J. Klippenstein, I. R. Sims, B. R. Rowe, J. Phys. Chem. Lett. 1, 2962 (2010).


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Cluster Aggregation, Spin Dynamics, and Cold Reactions

in Doped Helium Droplets

Wolfgang E. Ernst

Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, Graz, Austria

Droplets of about 104

helium atoms (HeN) represent a nanometer-sized superfluid medium of 0.4 K temperature and the least interacting matrix material for molecular spectroscopy. They can be doped with one or several atoms or molecules that move freely in or on the droplets and may form complexes in this cold environment. Very weakly bound species and even unusual conformers are observed and can be investigated with any method that is commonly applied to molecular beams: laser spectroscopy and ionization, mass spectrometry, spin resonance, measurements in external electric or magnetic fields.1 We studied the aggregation of metal clusters in helium droplets, with the goal to identify high and low spin states by measuring the circular dichroism in the presence of a magnetic field (MCD). In an optically detected electron resonance experiment, we determined hyperfine coupling, spin lifetimes and relaxation rates. The measurements were accompanied by our own quantum chemistry calculations. Results will be reported on the electron-nuclear coupling dynamics in alkali trimers2,3 and the formation of large alkali4 and chromium5 clusters. Interaction with surrounding helium causes fast vibrational1 and spin6 relaxation in molecules. Electronic excitation is sometimes followed by relaxation into metastable states.7 High resolution ESR spectroscopy8 of K and Rb on helium droplets shows the influence of the helium droplet size on the electron spin density at the alkali nucleus.9 The corresponding change of the Fermi contact interaction was modeled by a combination of ab initio methods and semiempirical scaling.10 ESR measurements also provide a sensitive probe for the influence of the helium solvent on the weak van der Waals interaction between two different dopants in or on a helium droplet, e.g. Xe inside and Rb outside HeN.11 The formation of alkali – alkaline earth diatomics is of interest to the ultracold molecule community. On helium droplets, we have recently observed electronic excitation spectra of LiCa and RbSr that will be reported at the conference.

1. C. Callegari and W. E. Ernst in: Handbook of High Resolution Spectroscopy, Eds. F. Merkt and M. Quack,

Vol. 3, p. 1551-1594, John Wiley & Sons, Chichester, 2011. 2. A. W. Hauser and W. E. Ernst, PCCP 13, 18762 (2011). 3. A. W. Hauser, G. Auböck and W. E. Ernst, in: Vibronic Interactions and the Jahn-Teller Effect : Theory and

Applications, (eds. M. Atanasov, C. Daul, P. Tregenna-Piggott), Springer Series: Progress in Theoretical Chemistry and Physics Vol. 23, Chapter 16, p. 301-316, Springer 2012.

4. M. Theisen, F. Lackner, and W. E. Ernst, J. Phys. Chem. A 115, 7005 (2011) 5. M. Ratschek, M. Koch, and W. E. Ernst, J. Chem. Phys. 136, 104201 (2012). 6. G. Auböck, J. Nagl, C. Callegari, and W. E. Ernst, J. Phys. Chem. A 111, 7404 (2007). 7. A. Kautsch, M. Hasewend, M. Koch, and W. E. Ernst, Phys. Rev. A 86, 033428 (2012). 8. M. Koch, G. Auböck, C. Callegari, and W. E. Ernst, Phys. Rev. Lett. 103, 035302 (2009). 9. M. Koch, C. Callegari, and W. E. Ernst, Mol. Phys. 108, 1005 (2010). 10. A. W. Hauser, T. Gruber, M. Filatov, and W. E. Ernst, ChemPhysChem 2013 (in print). 11. J. Poms, A. W. Hauser, and W. E. Ernst, PCCP 14, 15158 (2012).


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Electronically nonadiabatic interactions of free radicals at metal surfaces:

Does the unpaired electron matter?

Alec M. Wodtke

Georg-August University of Göttingen and Max Planck Institute for Biophysical Chemistry, Göttingen, Germany

Great strides in our understanding of surface chemistry have been achieved over the last two decades due to the advent of computational methods that rely on the Born-Oppenheimer Approximation and exploit the power of Density Functional Theory. Many experiments now show the breakdown of the Born Oppenheimer Approximation for molecular interactions at metal surfaces. Specifically Born-Oppenheimer breakdown is readily observed when the free-radical Nitric Oxide collides at a metal surface. Indeed, NO collisions at a Au(111) surface have now become one of the most heavily studied and best understood cases of Born-Oppenheimer breakdown for molecular interactions at surfaces. In this lecture, I will address the question to what degree the free radical character of NO determines the electronically nonadiabatic character of the interaction.

Related References: 1. T. Schäfer, N. Bartels, K. Golibrzuch, C. Bartels, H. Kockert, D. J. Auerbach, T. N. Kitsopoulos, A. M.

Wodtke, Phys. Chem. Chem. Phys. 15, 1863 (2013). 2. T. Schäfer, N. Bartels, N. Hocke, X. M. Yang, A. M. Wodtke, Chem. Phys. Letts. 535, 1 (2012). 3. R. Cooper, Z. S. Li, K. Golibrzuch, C. Bartels, I. Rahinov, D. J. Auerbach, A. M. Wodtke, J. Chem. Phys.

137, 064705 (2012). 4. R. Cooper, C. Bartels, A. Kandratsenka, I. Rahinov, N. Shenvi, K. Golibrzuch, Z. S. Li, D. J. Auerbach, J.

C. Tully, A. M. Wodtke, Angew. Chem. – Int. Ed. 51, 4954 (2012). 5. C. Bartels, K. Golibrzuch, A. Kandratsenka, R. Cooper, I. Rahinov, D. J. Auerbach, A. M. Wodtke, in 28th

International Symposium on Rarefied Gas Dynamics 2012, Vols. 1 and 2, M. Mareschal et al., Eds. (2012), vol. 1501, pp. 1330-1339.

6. I. Rahinov, R. Cooper, D. Matsiev, C. Bartels, D. J. Auerbach, A. M. Wodtke, Phys. Chem. Chem. Phys 13, 12680 (2011).

7. J. Larue, T. Schäfer, D. Matsiev, L. Velarde, N. H. Nahler, D. J. Auerbach, A. M. Wodtke, Phys. Chem. Chem. Phys 13, 97 (2011).

8. N. H. Nahler, J. D. White, J. Larue, D. J. Auerbach, A. M. Wodtke, Science 321, 1191 (2008). 9. J. D. White, J. Chen, D. Matsiev, D. J. Auerbach, A. M. Wodtke, Nature 433, 503 (2005). 10. Y. H. Huang, C. T. Rettner, D. J. Auerbach, A. M. Wodtke, Science 290, 111 (2000).


14

Ab initio Surface Photochemistry

Thorsten Klüner

Institute of Chemistry, University of Oldenburg, Carl-von-Ossietzky Str. 9-11, 26129

Oldenburg, Germany Photodesorption of small molecules from surfaces is one of the most fundamental processes in surface photochemistry. Despite its apparent simplicity, a microscopic understanding beyond a qualitative picture still poses a true challenge for theory. While the dynamics of nuclear motion can be treated on various levels of sophistication, all approaches suffer from the lack of sufficiently accurate potential energy surfaces, in particular for electronically excited states involved in the desorption scenario. In the last decade, we have developed a systematic and accurate methodology to reliably calculate accurate ground and excited state potential energy surfaces (PES) for different adsorbate-substrate systems1. These potential energy surfaces serve as a prerequisite for subsequent quantum dynamical wave packet calculations, which allow for a direct simulation of experimentally observable quantities such as velocity distributions. In this talk, I will focus on recent results obtained for photodesorption of NO and CO from a NiO(100) surface2,3. In contrast to previous studies, we were able to construct highly accurate potential energy surfaces based on correlated quantum chemical calculations (CASPT-2/CCSD(T)). Despite the enormous computational cost, this level of theory turns out to be crucial, since less sophisticated approaches such as density functional theory (DFT) cannot even provide a reliable description of ground state properties, not to mention electronically excited states. These potential energy surfaces were used in subsequent wave packet studies which reveal new desorption mechanisms. In the NO/NiO(100) case, we observed an anti-Antoniewicz scenario in which the wave packet is initially repelled from the surface but eventually reaches a turning point before it is back-scattered from the surface2. State resolved desorption velocity distributions have been calculated, and the results are in good agreement with experimental findings. In the CO/NiO(100) system, we observe the formation of a genuine covalent bond upon photoexcitation for the first time3. As demonstrated in the current study, this chemical bond formation is the crucial step in the desorption mechanism for this system. Again, our results are in good agreement with recent experiments. Recently, we extended our studies beyond a static surface wave packet jumping scenario and applied a Surrogate Hamiltonian approach to estimate the resonance lifetime of excited state intermediates by including a bath of electron-hole pairs coupled to the quantum system under investigation. This approach also allows us to treat the system, the bath or both within optimal control theory (OCT) including time-dependent targets4. In this talk, I will present first results and future perspectives. 1. T. Klüner, Prog. Surf. Sci. 85, 279 (2010). 2. I. Mehdaoui, D. Kröner, M. Pykavy, H.-J. Freund, T. Klüner, Phys. Chem. Chem. Phys. 8, 1584 (2006). 3. I. Mehdaoui, T. Klüner, Phys. Rev. Lett. 98, 037601 (2007). 4. E. Asplund, T. Klüner, Phys. Rev. Lett. 106, 140404 (2011).

Hot Topic H-02

15

Infrared Spectra of Protonated Pyrene and Coronene and Their Neutral

Counterparts in Solid Para-Hydrogen

Mohammed Bahou,a) Yu-Jong Wu,b) Yuan-Pern Lee a,c)

a) Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001, Ta-Hsueh Road, Hsinchu 30010, Taiwan

b) National Synchrotron Radiation Research Center, 101, Hsin-Ann Road, Hsinchu 30076, Taiwan

c) Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan Protonated polycyclic aromatic hydrocarbons (H+PAH) have been reported to have infrared (IR) bands at wavenumbers near those of unidentified infrared (UIR) emission bands from interstellar objects. However, recording IR spectra of H+PAH in laboratories is challenging, largely because of the difficulties in generating H+PAH in sufficient quantity for spectral interrogation. Two major spectral methods are employed to yield IR spectra of H+PAH. One employs IR multiphoton dissociation (IRMPD) of H+PAH, but the bands are broad and red-shifted.1 Another measures the single-photon IR photodissociation (IRPD) action spectrum of cold H+PAH tagged with a weakly bound ligand, such as Ar, but application of this method to large PAH is difficult.2 A new method for investigating IR spectra of H+PAH and their neutral counterparts was developed using electron bombardment during p-H2 matrix deposition. With this technique, we have obtained high-resolution IR spectra of protonated benzene (C6H7

+) 3 and naphthalene ( - and -C10H9

+),4 as well as their neutral counterparts. We produced 1-C16H11

+ and 1-C16H11 upon electron bombardment during matrix deposition of p-H2 containing pyrene (C16H10) in a small proportion. Intensities of absorption features of 1-C16H11

+, with intense lines at 1618.0, 1540.2, 1391.3, 1341.7, 1230.2, and 868.9 cm 1, decreased after the matrix was maintained in darkness or irradiated with light at 365 nm, whereas those of 1-C16H11, with intense features at 2839.7, 1552.3, 1410.3, 839.7, 811.8, and 654.4 cm 1, increased. Similarly, we produced 1-C24H13

+ and 1-C24H13 upon electron bombardment of p-H2 containing coronene (C24H12) in a small proportion. Intensities of absorption features of 1-C24H13

+, with intense lines at 1619.7, 1546.8, 1375.7, 1356.7, 1327.2, 1218.5, and 874.0 cm 1, decreased after the matrix was maintained in darkness or irradiated with light at 365 nm, whereas those of 1-C24H13, with intense features at 1293.6, 822.4, 847.2/851.1, and 541.0 cm 1, increased. Lines of 1-C24H13 were also observed upon photolysis of a C24H12/Cl2/p-H2 matrix with UV and IR light to initiate the reaction H + C24H12. The observed line wavenumbers and relative intensities of these protonated species and their neutral counterparts agree satisfactorily with the scaled vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++G(2d, 2p) method. Our method, being relatively clean with negligible fragmentation, is applicable to larger H+PAH; it has the advantages of producing excellent IR spectra covering a broad spectral range with narrow lines and accurate intensities, so that structural identification among various isomers is feasible. 1. H. Knorke, J. Langer, J. Oomens, O. Dopfer, Astrophys. J. Lett. 706, L66 (2009). 2. A. M. Ricks, G. E. Douberly, M. A. Duncan, Astrophys. J. 702, 301 (2009). 3. M. Bahou, Y.-J. Wu, Y.-P. Lee, J. Chem. Phys. 136, 154304 (2012). 4. M. Bahou, Y.-J. Wu, Y.-P. Lee, Phys. Chem. Chem. Phys. 15, 1907 (2013).


16

Reaction Dynamics of Oxygen Atoms with Unsaturated Hydrocarbons: Primary Radical and Molecular Products, Branching Ratios and Role of

Intersystem Crossing

P. Casavecchia, F. Leonori, N. Balucani

Dipartimento di Chimica, Università degli Studi di Perugia, Via Elce di Sotto, 8, 06123 Perugia, Italy

Small unsaturated hydrocarbons, such as C2H2 (acetylene), C2H4 (ethylene) and C3H4 (allene and methylacetylene), are crucial intermediates in hydrocarbon combustion, where their dominant consumption pathways are reactions with ground-state oxygen atoms, O(3P). These reactions are characterized by a variety of energetically open, competing radical and molecular product channels, some of which can take place only via intersystem crossing (ISC) from triplet to singlet potential energy surfaces (PES). In combustion modelling, among the most important information needed for each of these elementary multichannel reactions of O(3P) are: (a) the overall rate constant, (b) the identity of the primary products, and (c) the branching ratios (BRs) possibly as a function of collision energy Ec (temperature). While kinetics experiments are able to satisfy point (a), point (b) and (c) still represent a challenge for kinetics, although considerable progress has recently been made1. The method most suitable to tackle this challenge is the crossed molecular beams (CMB) scattering technique with “universal” mass spectrometric detection based on “soft” ionization by tunable energy electrons2 or VUV synchrotron radiation3. In this talk we will report on our recent investigations of the reaction dynamics of O(3P) with acetylene4, ethylene5, allene6 and methylacetylene7 using the CMB method. By exploiting “soft” electron-ionization we have probed all energetically allowed product channels (up to ten in O + C3H4) and characterized the dynamics, branching ratios and extent of ISC. The BRs for the five competing channels leading to H + CH2CHO, H + CH3CO, H2 + CH2CO, CH3 + HCO, and CH2 + HCHO from O + C2H4 are analyzed together with those obtained from kinetics studies at room temperature8 (Ec 0.9 kcal/mol). The combined kinetics and dynamics results have allowed us to examine the BRs and the extent of ISC in a wide range of Ecs (temperature), from ~1 kcal/mol (300 K) up to ~13 kcal/mol (4300 K). Experimental results are compared with those of available statistical calculations on ab initio PESs for all systems and with those of quasiclassical trajectory surface-hopping computations carried out in a synergic fashion by the group of Bowman on coupled ab initio triplet and singlet PESs for the benchmark multichannel nonadiabatic reaction O + C2H4. ISC is found to increase strongly with molecular complexity (from about 0 % in O + C2H2 up to about 50 % in O + C2H4 and more than 90 % in O + CH2CCH2) and to depend on molecular structure (about 80 % in O + CH3CCH). Acknowledgment: Support from MIUR (PRIN 2010-2011) and EC COST Action CM0901 “Detailed Chemical Models for Cleaner Combustion” is gratefully acknowledged.

1. D. Savee, O. Welz, C. A. Taatjes, D. L. Osborn, PCCP 14, 10410 (2012). 2. P. Casavecchia et al., PCCP 11, 46 (2009) (Perspective); JPC A 109, 3527 (2005). 3. S.-H. Lee, W.-K. Chen, W.-J. Huang, J. Chem. Phys. 130, 054301 (2009). 4. G. Capozza et al. JCP 120, 4557 (2004); F. Leonori, N. Balucani, P. Casavecchia et al. (in preparation). 5. B. Fu, J. M. Bowman, P. Casavecchia et al. PNAS 109, 9733 (2012); JCP 137, 22A532 (2012); and (in

preparation). 6. F. Leonori, N. Balucani, P. Casavecchia et al., J. Phys. Chem. Lett. 3, 75 (2012). 7. P. Casavecchia et al. (in preparation). 8. T. L. Nguyen, et al., JPC A, 109, 7489 (2005); A. Miyoshi et al., PCCP 11, 7318 (2009).


17

Defying and Ducking Intrinsic Reaction Coordinates:

Experiments and Theory on Radical Intermediates

Laurie J. Butler

Department of Chemistry and the James Frank Institute The University of Chicago

Radical intermediates play a key role in a wide range of atmospheric, combustion, and synthetic processes. Spectroscopic studies of radical species reveal their structures, but the multiple competing decomposition product channels of polyatomic radical intermediates have hindered investigations of their reaction kinetics and dynamics. Our velocity map imaging and molecular beam scattering experiments allow us to definitively study the product branching from radicals with internal energies characteristic of intermediates along bimolecular reaction coordinates. The talk focuses on studies of two radical intermediates, one important in the mechanism for oxidation of atmospheric unsaturated hydrocarbons and the other important in the decomposition mechanism of geminal di-nitro energetic materials. We present experimental results and their analysis with transition state theory, sketch map, and quasi-classical trajectory calculations, the latter two facilitated by our collaborators Joel Bowman and Michele Ceriotti.


18

HO2 radicals everywhere, but how to detect them?

Christa Fittschen

PhysicoChimie des Processus de Combustion et de l’Atmosphere, University Lille 1, Cité

Scientifique, Bât. C11, Villeneuve d’Ascq, France HO2 radicals are key species in oxidation processes under atmospheric conditions, but also under low temperature combustion condition (T < 1000 K). Their concentration is often closely linked to the concentration of OH radicals and therefore it is desirable to detect both species simultaneously. A time resolved detection is needed for studying the reactivity of both radicals, while the quantification is desired during field campaigns, organized to better understand the chemistry that governs the removal of trace gases in different environments. The selective and sensitive detection of OH radicals is possible through laser induced fluorescence (amongst others), whereby a calibration is needed to obtain absolute concen-trations. The task is more difficult for HO2 radicals: these radicals being non-fluorescing, much work has been carried out using the rather non-selective UV-absorption spectroscopy1. The overtone of the more selective O−H stretch near 1.5 μm has been exploited by different groups for a detection of HO2 radicals2. Very recently, Faraday rotation spectroscopy in the mid-infrared has been employed to detect HO2 in-situ in a reactor under combustion conditions3. We have developed in Lille two different experiments for the simultaneous detection of both radicals: - Laser photolysis coupled to in-situ detection of HO2 radicals by cw-CRDS at around

1.5µm and OH radicals by high repetition rate (10 kHz) LIF4

- A FAGE set-up, i.e. detection of OH and HO2 (after conversion to OH by fast reaction with NO) by high repetition rate LIF after rapid expansion to low pressure ( 1 Torr).5

Different application of both set-ups linked to atmospheric and combustion chemistry will be presented at the conference. 1. e.g., R. X. Fernandes, K. Luther, J. Troe, and V. G. Ushakov, Phys. Chem. Chem. Phys. 10, 4313 (2008); M.

Sangwan,L. N. Krasnoperov, J. Phys. Chem. A 117, 2916–2923 (2013); Z. Hong, D. F. Davidson, K.-Y. Lam, and R. K. Hanson, Combust. Flame 159, 3007 (2012).

2. e.g., J. D. DeSain, A. D. Hob, and C. A. Taatjes, J. Mol. Spectrosc. 219, 163 (2003); L. E. Christensen, M. Okumura, S. P. Sander, R. R. Friedl, C. E. Miller, and J. J. Sloan, J. Phys. Chem. A 108, 80 (2004).

3. B. Brumfield, W. Sun, Y. Ju, and G. Wysocki, J. Phys. Chem. Lett., 872 (2013). 4. J. Thiebaud,C. Fittschen, Appl. Phys. B: Lasers and Optics 85, 383 (2006); A. Parker, C. Jain, C.

Schoemaecker, P. Szriftgiser, O. Votava, and C. Fittschen, Appl. Phys. B: Lasers and Optics 103, 725 (2011). 5. D. Amedro, A. E. Parker, C. Schoemaecker, and C. Fittschen, Chem. Phys. Lett. 513, 12 (2011); D. Amedro,

K. Miyazaki, A. Parker, C. Schoemaecker, and C. Fittschen, J. Environ. Sci. 24, 78 (2012).


19

Climate Change, Biomass energy, and Organic Radicals

Barney Ellison,a) Mark R. Nimlos,b) Musahid Ahmed,c) John W. Daily,d) John F. Stanton e)

a) Dept. Chem. & Biochem, Univ. Colorado, Boulder, 80309-0215 b) NREL, 1617 Cole Blvd., Golden, CO 80401

c) Chemical Sciences Division, LBNL MS 6R-2100, Berkeley CA 94720 d) Department of Mechanical Engineering, Univ. Colorado, Boulder, CO 80309-0427

e) Institute for Theoretical Chemistry, Univ. Texas, Austin, TX 78712 Climate Change and the world’s energy crisis are inextricably linked. Because of this connection, the world must find replacements for roughly 90 % of all the energy we now depend on. Biomass from vegetation is the only renewable source of carbon-based transportation fuels and chemicals for manufacturing. To understand the thermal decomposition mechanisms of biomass, we are developing a tiny furnace to study the thermal cracking of complex organic molecules. We use a heated 0.5 mm × 2 cm SiC microtubular reactor to decompose biomass monomers such as aldehydes, ketones, and alkylaryl ethers.

Thermal decomposition of 0.01 % samples mixed with He or Ar carrier gases takes place at pressures of 75 – 250 Torr and at temperatures up to 1700 K. Residence time of the organics in the reactor is roughly 100 – 200 µsec. The organic decomposition products are identified by three independent techniques: VUV photoionization mass spectroscopy (PIMS), resonance enhanced multiphoton ionization (REMPI), and infrared (IR) absorption spectroscopy after isolation in a cryogenic matrix. The thermal cracking of aromatics such as furan, furfural, methoxybenzene, and guaiacol (HOC6H4OCH3) will be discussed.


20

Vibrationally Resolved Dynamics of Free Radical Reactions in Solution

A. J. Orr-Ewing,a) G. T. Dunning,a) F. Abou-Chahine,a) D. R. Glowacki,a) J. N. Harvey,a) S. J.

Greaves,b) I. P. Clark,c) G. M. Greetham,c) M. Towrie c)

a) School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK b) School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, UK

c) Central Laser Facility, STFC, Rutherford Appleton Laboratory, Didcot, UK The dynamics of free radical reactions in the gas phase can be examined in considerable detail using techniques such as velocity map imaging, which afford product ro-vibrational quantum state resolution. Whether the deep understanding gained from such studies under isolated collision conditions can be translated to reactions in liquids remains an open question, however. We have sought to explore the effect of a liquid environment on the chemical dynamics by examining the reactions of F atoms, Cl atoms and CN radicals with various organic molecules in common solvents such as chloroform or acetonitrile. In the gas phase, these exothermic abstraction reactions have early transition states that favour vibrational excitation of newly formed reaction products. Complementary study of such reactions in solution provides an opportunity to examine how the solvent modifies reactive potential energy surfaces and how the associated reaction dynamics change in a highly collisional environment. Time-resolved infra-red absorption spectroscopy allows us to search for evidence of product vibrational excitation, but requires picosecond time resolution to compete with relaxation of any such vibrationally excited products by loss of excess energy to the surrounding solvent bath. We have previously reported observation of vibrationally excited HCN (and DCN) from the reactions of CN radicals with cyclohexane (and d12-cyclohexane) in various solvents.1-4 The vibrational excitation is initially localized in the C-H stretch and bending excitations, and computational simulations not only reproduce the observed dynamics, but also provide important new insights concerning energy flow from the vibrationally hot reaction products.5 These studies have since been extended to exothermic reactions of Cl and F atoms in various organic solvents,6 for which we are also able to quantify branching to vibrationally excited products and the timescales for relaxation by coupling to the solvent. 1. S.J. Greaves, R.A. Rose, T.A.A. Oliver, D.R. Glowacki, M.N.R. Ashfold, J.N. Harvey, I.P. Clark, G.M.

Greetham, A.W. Parker, M. Towrie and A.J. Orr-Ewing, Science, 331, 1423 (2011). 2. A.J. Orr-Ewing, D.R. Glowacki, S.J. Greaves and R.A. Rose, J. Phys. Chem. Lett. 2, 1139 (2011). 3. R.A. Rose, S.J. Greaves, T.A.A. Oliver, I.P. Clark, G.M. Greetham, A.W. Parker, M. Towrie, and A.J. Orr-

Ewing, J. Chem. Phys. 134, 244503 (2011). 4. R.A. Rose, S.J. Greaves, F. Abou-Chahine, D.R. Glowacki, T.A.A. Oliver, M.N.R. Ashfold, I.P. Clark, G.M.

Greetham, M. Towrie and A.J. Orr-Ewing, PCCP 14, 10424-10437 (2012). 5. D.R. Glowacki, R.A. Rose, S.J. Greaves, A.J. Orr-Ewing and J.N. Harvey, Nature Chem. 3, 850 (2011). 6. S.J. Greaves, G.T. Dunning, A.J. Orr-Ewing, G.M. Greetham, I.P. Clark, and M. Towrie, Chem. Sci. 4, 226-

237 (2013).


21

Polymerization processes understood via the kinetics of

elementary radical reactions

Michael Buback

Institute for Physical Chemistry, University of Göttingen, D-37077 Göttingen, Tammannnstraße 6, Germany ([email protected])

Simulation of radical polymerization kinetics and of molar masses of the resulting polymer requires accurate knowledge of the underlying rate coefficients, e.g., of initiation, propa-gation, transfer and termination as a function of polymerization temperature, pressure, monomer conversion, and solvent environment. The advent of pulsed-laser (PL)-assisted techniques has enormously improved the quality by which the relevant rate coefficients may be accurately measured. Pulsed laser polymerization–size-exclusion chromatography (PLP–SEC) has become the method of choice for measuring propagation rate coefficients, kp, in bulk and in solution. PLP induced by a laser single pulse (SP) in conjunction with highly time-resolved near-infrared spectroscopic analysis of the resulting monomer conversion has turned out to be well suited for measuring radical termination kinetics as a function of degree of monomer conversion. The recently developed SP–PLP–EPR technique is even more powerful. The decay of radical concentration after applying an intense laser SP may be directly monitored via time-resolved electron paramagnetic resonance (EPR) spectroscopy at a time resolution of microseconds. Examples of the resulting very detailed picture of diffusion-controlled termination will be presented with emphasis on the composite model for chain-length dependent termination. The SP–PLP–EPR method allows for studying systems which contain more than one type of radicals, e.g., acrylate polymerization, in which secondary chain-end radicals may undergo so-called backbiting processes via a six-membered cyclic transition-state structure to produce tertiary mid-chain radicals with very different kinetic properties. SP–PLP–EPR also allows for detailed kinetic studies into “controlled” radical polymerizations, such as ATRP (atom transfer radical polymerization) and RAFT (reversible addition fragmentation transfer) polymerization. Both are versatile techniques for producing polymer of defined size and architecture.

H-03 Hot Topic

22

Resonance stabilized radicals from H addition to aromatic rings

O. Krechkivska, T. P. Troy, C. Wilcox, G. D. O’Connor, K. Nauta, S. H. Kable,

T. W. Schmidt

aSchool of Chemistry, The University of Sydney, NSW 2006, Australia In the course of studies on the products of electrical discharges through argon containing aromatic compounds, we have observed a tendency for H atoms to add to aromatic rings. Thus far, we have obtained resonant 2-colour 2-photon ionization spectra of the products of H + benzene, H + toluene and H + phenol. Curiously, even when working with completely deuterated precursors, only H atoms were found to add. Further investigation found the source of H atoms to be due to traces of water in the gas lines, as addition of D2O yielded the desired deuterated products. From H + benzene, the cycloheadienyl radical is produced, which has been studied previously.1,2,3 Our new spectra allowed for the accurate determination of the ionization energy, which in turn firms up the gas phase proton affinity of benzene, in conjunction with the theoretical bond dissociation energy.1 At threshold, vibrationally (very) cold protonated benzene is produced, in situ, allowing its study by laser spectroscopy. Addition of H to toluene activates the ring to further attack, and may be an important reaction in the combustion of fossil fuels. Our investigations of ionization energies and spectra infer that addition is most favorable at the ortho position. The spectra are (pleasantly) complicated by the methyl rotor dynamics. Addition of H to phenol yields a C6H6OH product which may have a role to play on the atmospherically important benzene + OH surface. Analysis of the spectra reveals the appearance of two conformers of the ortho addition product, similarly to toluene. 1. A. Bargholz, R. Oswald and P. Botschwina, J. Chem. Phys. 138, 014307 (2013). 2. M. Nakajima, T.W. Schmidt, Y. Sumiyoshi, Y. Endo, Chem. Phys. Lett. 449, 57 (2007). 3. T. Imamura, W. Zhang, H. Horiuchi, H. Hiratsuka, T. Kudo, and K. Obi, J. Chem. Phys. 121, 6861 (2004).


23

Electron attachment to fluorocarbon radicals

Nicholas S. Shuman,a) Thomas M. Miller,a) Albert A. Viggiano,a) Jürgen Troe b)

a) Air Force Research Laboratory, Space Vehicles Directorate, 3550 Aberdeen Ave. SE,

Kirtland Air Force Base, NM, USA b) Institut fur Physikalische Chemie, Universität Göttingen, Göttingen, Germany

Max-Planck-Institut für Biophysikalische Chemie, Göttingen, Germany Most plasma environments contain populations of short-lived species such as radicals, the chemistry of which can have significant effects on the overall chemistry of the system. However, few experimental measurements of the kinetics of electron attachment to radicals exist due to the inherent difficulties of working with transient species. Calculations from first principles have been attempted, but they are both exceptionally arduous and, because electron attachment is so sensitive to the specifics of the potential surface, their accuracy has not been established. Electron attachment to small fluorocarbon radicals is particularly important, as the data are needed for predictive modeling of plasma etching of semiconductor materials, a key process in the industrial fabrication of microelectronics.

We have recently developed a novel flowing afterglow technique to measure several types of otherwise difficult to study plasma processes, including thermal electron attachment to radicals. Variable Electron and Neutral Density Attachment Mass Spectrometry (VENDAMS) exploits dissociative electron attachment in a weakly ionized plasma as a radical source. Here, we apply VENDAMS to a series of halofluorocarbon precursors in order to measure the kinetics of thermal electron attachment to fluorocarbon radicals.1 Results are presented for CF2, CF3, C2F5, CF3, 1-C3F7, 2-C3F7, and C3F5 from 300 K to 900 K.2 Both the magnitude and the temperature dependences of rate coefficients as well as product branching between associative and dissociative attachment are highly system specific; however, thermal attachment to all species is inefficient, never exceeding 5 % of the collision rate.

The data are analyzed using a recently developed kinetic modeling approach, which uses extended Vogt-Wannier theory as a starting point, accounts for dynamic effects such as coupling between the electron and nuclear motions through empirically validated functional forms, and finally uses statistical theory to determine the fate of the highly excited anion intermediate formed during attachment. The kinetic modeling, along with complimentary data from electron beam measurements,3 is used to extrapolate the electron attachment rate coefficients to temperature and pressure regimes inaccessible to the experiment, including to non-thermal plasma conditions most relevant to plasma etching.4 1. N. S. Shuman, T. M. Miller, J. F. Friedman, A. A. Viggiano, A. I. Maergoiz, and J. Troe, J. Chem. Phys. 135,

054306 (2011). 2. N. S. Shuman, T. M. Miller, and A. A. Viggiano, J. Chem. Phys. 137, 214318 (2012). 3. S. A. Haughey, T. A. Field, J. Langer, N. S. Shuman, T. M. Miller, J. F. Friedman, and A. A. Viggiano, J.

Chem. Phys. 137, 054310 (2012). 4. N. S. Shuman, T. M. Miller, A. A. Viggiano, and J. Troe, J. Chem. Phys. 138, in press (2013).

H-04 Hot Topic

24

Reactions of state-selected O+ cations and nitrile anions

of interest for astrochemistry

C. Romanzin,a) B. Cunha de Miranda,a,b) S. Chefdeville,a,c) E. Louarn,a) J. Lemaire,a) J. Zabka,d) M. Polasek,d) V. Vuitton,e) C. Alcaraz a,b)

a) Lab. de Chimie Physique, Bât 350, UMR 8000 CNRS-Université Paris-Sud, Orsay, France

b) Synchrotron SOLEIL, L'Orme des Merisiers, Saint Aubin, France c) ISM, UMR 5255 CNRS-Université Bordeaux I, Talence, France

d) J. Heyrovsky Inst. of Physical Chemistry of the ASCR, Prague, Czech Republic e) Institut de Planétologie et d'Astrophysique de Grenoble, UMR 5274, Grenoble, France

Titan, Saturn’s largest moon, exhibits a dense atmosphere characterized by a thick orange haze and mainly composed of molecular nitrogen and methane as well as numerous other organic compounds such as nitriles. The chemistry taking place in its atmosphere is complex and still not completely understood. Yet, results from the Cassini-Huygens mission have shown that ionospheric chemistry must play a more important role than previously thought. The discovery of CN-, C3N- and C5N- together a large amount of heavy cations and anions in the upper atmosphere1,2 came indeed as a surprise and suggests that they contribute to the formation of aerosols particles. The detection of an O+ flux precipitating in the upper atmosphere also suggests new pathways for the oxygen chemistry3. In this context, we have undertaken experimental investigations of several relevant ion-molecule reactions: O+ with CH4 and C2H4 and CN- and C3N- with HC3N.

The reaction of state-selected O+(4S, 2D, 2P) ions with methane have been studied on the guided ion beam apparatus, CERISES4. The O+ ions are produced by dissociative photoionisation of O2 and pure-state selection is achieved by means of a double threshold technique. Experiments are performed on the DESIRS VUV beamline at the synchrotron SOLEIL. Absolute cross sections for the ionic products formation have been measured as a function of electronic excitation of O+ and collision energy. The results obtained are consistent with previous work5 on the reaction of ground state O+(4S) but highlights large differences (cross-section, branching ratios) with excitation of O+ to the 2D and 2P states.

In a first experiment, the CN- + HC3N reaction has been studied in a tandem mass spectrometer as a function of the HC3N target pressure in order to explore different collisional conditions. CN- parent anions were produced from CH3CN by chemical ionization. The primary and secondary reactions with HC3N are found to be extremely efficient, resulting in anionic products of rapidly growing size. A detailed mechanism for the growth of these species is proposed and its relevance to the growth of heavy anions in Titan's ionosphere is discussed.6 Then, to probe the kinetics of individual steps of this growth, the reactions of CN- and C3N- with HC3N have been then studied in a FT-ICR setup7 at low HC3N target pressure. 1. A.J. Coates et al., Geophys. Res. Lett. 34, L22103 (2007). 2. V. Vuitton et al., Planet. Space Sci. 57, 1558 (2009). 3. S.M. Hörst et al., J. Geophys. Res. 113, E10006 (2008). 4. C. Alcaraz et al., J. Phys. Chem. A 108, 9998 (2004). 5. D.J. Levandier et al., J. Phys. Chem. A 108, 9794 (2004). 6. J. Žabka et al., Icarus 219, 161 (2012). 7. G. Mauclaire et al., Eur. J. Mass Spectrom. 10, 155 (2004).

Hot Topic H-05

25

Threshold Photoelectron-Photoion Coincidence Spectroscopy of the Nitrate

Cation NO3+ Studied by Vacuum Ultraviolet Synchrotron Radiation

Kana Takematsu,a) Gustavo Garcia,b) Laurent Nahon,b) John Stanton,c) Mitchio Okumura a)

a) Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125 USA

b) Synchrotron SOLEIL, L’Orme des Merisiers, St Aubin, BP 48, 91192 Gif sur Yvette Cedex, France

c) Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712, USA

The Jahn-Teller (JT) Effect is of fundamental importance in molecular physics. Spontaneous symmetry breaking occurs at a symmetry-allowed “conical intersection” (CI) of two potential energy surfaces, i.e. a point in the multidimensional space of nuclear coordinates where two or more surfaces intersect. Simple tri-oxides such as NO3 and CO3 are quantitative tests of accurate ab initio methods to compute conical intersections. The NO3

+ cation offers fascinating possibilities for examining the Jahn-Teller Effect. It is a simple cation – isoelectronic with CO3 – that should be amenable to high level calculations.While the ground state, with an IP = 12.55 eV, is a nondegenerate symmetric state (1A1’) and hence not subject to the JT Effect, theoretical calculations indicate that there are three low-lyingexcited electronic states of E symmetry (two triplets and one singlet). These states are then all subject to the Jahn-Teller effect, as well as to nonadiabatic couplings among all states in the manifold. There have been two low resolution experiments, first by photoionization mass spectroscopy (PIMS)1 and then by He I photoelectron spectroscopy (PES)2 of NO3. There is an unresolved controversy concerning the assignment of the excited states, which theory has attempted to address.3,4 While there is no evidence for excited states in the PIMS experiment, the PES spectrum reveals peaks assigned to excited states of NO3

+. However, large background contributions in the PES experiment – arising from high concentrations of precursors (N2O5 and NO2) – have raised concerns about the assignments. We report preliminary studies on the Threshold PhotoElectron-PhotoIon Coincidence (T-PEPICO) spectrum of the radical cation NO3

+ using the DELICIOUS3 coincidence spectrometer on the DESIRS beamline at the Soleil Synchrotron. This powerful technique allows us to identify the transitions to the excited states, as well as to extract the NO3

+ signal from the ionization of the dominant background species NO2 and N2O5. We report preliminary PEPICO and threshold PE spectra, recorded over the 12.5-14.5 eV range, that promise to shed light on the Jahn-Teller Effect in this system. 1. P. S. Monks, L. J. Stief, M. Krauss, S. C. Kuo, Z. Zhang, and R. B. Klemm, J. Phys. Chem. 98, 10017-10022

(1994). 2. D. Wang , P. Jiang , X. Qian , and G. Y. Hong, J. Chem. Phys. 106, 3003 (1997). 3. D. Heryadi and D. L. Yeager J. Chem. Phys. 108, 1292 (1999). 4. M. Wladyslawski and M. Nooijen, in Low-Lying Potential Energy Surfaces, (eds. Hoffmann, MR; Dyall,

KG), ACS Symposium Series, 828, 65 (2002).


26

New Multireference Electronic Structure Methods

Hans-Joachim Werner

Institute for Theoretical Chemistry, University of Stuttgart,

Pfaffenwaldring 55, D-70569 Stuttgart

Recent developments of multireference electron correlation methods in our group are reviewed. In particular, we will focus on new explicitly correlated multireference perturbation theory and multireference configuration interaction methods.1,2 The explicitly correlated (F12) terms very much reduce the basis set incompleteness errors, and typically at least quintuple-zeta quality is achieved already with triple-zeta basis sets. The additional cost is negligible. Benchmarks are presented for ground and excited states and various properties of molecules and elementary reactions. Furthermore, new implementations of analytic energy gradients for state-averaged CASSCF and CASPT2 wave functions3 that employ density fitting techniques to speed-up the evaluation of the two-electron integrals are presented. Finally, some applications to open-shell transition metal complexes with complicated electronic structure are discussed.

1. K. R. Shamasundar, G. Knizia, and H.-J. Werner, J. Chem. Phys. 135, 054101 (2011). 2. For a review and further references see: T. Shiozaki and H.-J. Werner, Mol. Phys. 111, 607 (2013). 3. W. Györffy, T. Shiozaki, G. Knizia, and H.-J. Werner, J. Chem. Phys. 138, 104104 (2013).


27

Rotational and Electronic Relaxation of the

CH2 Radical in Collisions with He

Millard H. Alexander,a) Lifang Ma,a) Paul J. Dagdigian b)

a) Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742-2021, USA

b) Department of Chemistry, The Johns Hopkins University, Baltimore, MD, 21218-2685, USA We report the investigation of the relaxation of the methylene radical, an important combustion intermediate, in its ground (X

3B1) and its first excited (ã

1A1) states. We have carried out exact quantum scattering calculations based on accurate ab initio potential energy surfaces (PESs) determined from high-level coupled-cluster calculations with inclusion of all single, double, and (perturbatively) triple excitations. For the ground state, where the barrier to inversion is low, the calculated PES was averaged over the bending vibrational wave function. The spin of the electronic ground state is ignored in the scattering calculations but can be added back in by a simple recoupling procedure. Except in the lowest levels, there is a strong propensity for conservation of the relative orientation of N and S. The relative magnitudes of the calculated cross sections for rotational relaxation both within and across K stacks (the manifolds associated with different body-frame projection quantum numbers) can be interpreted in a straightforward manner in terms of the dominant anisotropies of the PESs. Most notably, the electronic occupancy in the ã state, in which the out-of-plane 1b1 orbital is empty, results in an amphoteric interaction with the He atom. This gives rise to significantly stronger inelastic cross sections than for collision with CH2 in the X state. Good agreement is seen with the total ã state relaxation cross sections measured by Hall and Sears at Brookhaven.1 There exist a few accidental degeneracies between the ro-vibrational levels of the X and ã states. Significant mixing between these levels allows inelastic transitions between these two states of different multiplicity. This was first investigated experimentally by Bley and Temps.2 We will present a careful analysis of the efficiency of the additional relaxation pathways enabled by these “gateway” states. Acknowledgment: Research supported by the U. S. Department of Energy. 1. S. K. Lee, Y. Kim, T. J. Sears, and G. E. Hall (private communication). 2. U. Bley and F. Temps, J. Chem. Phys. 98, 1058 (1993).

H-06 Hot Topic Talk

28

Rotational Spectra in Service of Particle Physics:

Zeeman & Hyperfine Effects

R. J Mawhorter,a) A. L. Baum,a) Z. Glassmann,a) B. Girodas,a) T. Sears,b) N. E. Shafer-Ray,c) L. Alphei,d) J.-U. Grabow d)

a) Department of Physics and Astronomy, Pomona College, Claremont CA, USA

b) Chemistry Department, Brookhaven National Laboratory, Upton NY, USA c) Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma,

Norman OK, USA d) Institut für Physikalische Chemie und Elektrochemie, Gottfried-Wilhelm-Leibniz-

Universität, Hannover, Germany Motivated by the ongoing search for the parity violating effects originated by an electron electric dipole moment (e-EDM) or a nuclear anapole moment, the rotational spectra of heavy atom diatomic radicals like, e.g., 2

1/2 PbF are studied at the unrivalled resolution offered by supersonic-jet Fourier transform microwave spectroscopy. Obtaining accurate information on such relativistically behaving systems will be the key to provide a delicate test to the proposed theories in extension to the Standard Model of Physics. Employment of an MW method to hunt down these tiny effects, easily obscured by the line width inherent to other techniques, in rotational transitions is a promising approach to observe the tiny energy difference of terms that are degenerate without parity violation. Already before an experiment sensitive to parity violation, the exceptional resolution of the microwave time-domain technique can be exploited to provide accurate tests on the quantum chemical predictions that are part of the calculation of the anticipated e-EDM or anapole moment sensitivity of a given species since nuclear quadrupole and magnetic hyperfine effects in the rotational spectra are closely related. In our current experiment, transitions can be observed with 0.2 kHz accuracy for unblended lines over a range of 2 – 26.5 GHz. The observation of field dependent spectra (in magnetic fields up to 4 Gauss) allows for the determination of the two body fixed g-factors, G and G which can then be compared with recent theoretical values. YbF provides the current e-EDM upper limit. Although it is more sensitive to magnetic fields, the nuclear quadrupole hyperfine structure of 173YbF constitutes a direct probe on the electric field gradient and thus can help characterize the critical electric field at the heavy atom nucleus. We will report on 14 GHz transitions for 3 of the less abundant even isotopologues of YbF as well as the 207PbF analogue 171YbF, important steps towards observing 173YbF.


29

High-resolution Studies of Photodissociation Dynamics of

Polyatomic Free Radicals

Jingsong Zhang

Department of Chemistry and Air Pollution Research Center, University of California, 900 University Ave, Riverside, CA 92521, USA

The photodissociation dynamics of two prototypical polyatomic free radicals, methyl (CH3) radical and formyl radical (HCO), are investigated using the high-resolution high-n Rydberg atom time-of-flight (HRTOF) technique. In the ultraviolet (UV) photodissociation of jet-cooled methyl radical via its first electronically excited state B2A1' at 216.3 nm, the H + CH2 product translational energy distribution shows that CH2 is produced exclusively in the ground vibrational level of the ã1A1 state with modest rotational excitation, in agreement with previous studies. A negative anisotropy parameter is observed, consistent with the perpendi-cular B2A1' X2A2" transition (excitation of 2pz electron to 3s Rydberg orbital) at 216.3 nm and a fast dissociation by tunneling. The rotational structure of the CH2 (ã1A1, v = 0) product is resolved for the first time, providing detailed information of the tunneling dissociation dynamics. The UV photodissociation of partially rotationally resolved CD3 radical is also investigated, showing similar tunneling dissociation dynamics. The Ã2A" X2A' predissociation dynamics of the formyl radical is studied at a nearly state-to-state level in the visible region. The complete CO (v, J) product state distributions (including low J) are obtained in the H-atom product translational energy spectra. The CO product rotational distributions are highly inverted, in agreement with previous studies. Furthermore, intensity oscillations at high J states in the rotational distributions of CO are observed. The H-atom product angular distributions are also measured. Detailed predissociation dynamics will be discussed.


30

Radical, Triplet, Molecular, Roaming and Triple Fragmentation Pathways

in H2CO: Quantum Yields and Dynamics Across ~1 eV of Excitation

Mitchell S. Quinn, Gabrielle de Wit, Duncan U Andrews, Kin Long Kelvin Lee, Klaas Nauta, Meredith J. T. Jordan, S. H. Kable

School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia

The dynamics and quantum yields for radical and molecular pathways in the photo-dissociation of H2CO via its S1 state have been investigated for more than 40 years. There are 5 reaction channels, shown below, with thresholds indicated

H2CO + h H2 + CO (“TS channel”, 27700 cm−1) (1) H2 + CO (“roaming channel”, 30120-30240 cm−1) (2) H + HCO (“radical channel”, 30327.6 cm−1) (3) H + HCO (“triplet channel”, 31900 1000 cm−1) (4) H + H + CO (“3F”, 36070 cm−1, including 700 cm−1 barrier) (5)

The photodissociation dynamics of the first 4 pathways are well understood. We report here on a recently completed experimental and theoretical study of (5), probing both H and CO using ion imaging and 2-D REMPI spectroscopy (Fig. 1). In measuring pathway 5, we also revisited pathways 1-4 to learn about the importance of (5) in comparison to the others.

Triple fragmentation (3F) produces two speed components in the H fragment. The first H is fast, while spontaneous, secondary dissociation produces slow H, and CO with low J. The triplet channel (4) peaks in importance near threshold, then slowly diminishes with increasing energy in favour of (3). Roaming (2) and TS (1) are seen at all energies, with roaming slowly increasing over TS as energy increases. 3F increases rapidly above its threshold.

The relative quantum yields for (1) and (2), 1 and 2, are readily measured by probing CO. Similarly 3 vs 4 can be measured by monitoring H or HCO. Detection of H and CO above the 3F threshold connects the radical and molecular pathways. Detection of H provides evidence for (3), (4) and (5), while detection of CO probes (1), (2) and (5). Therefore the quantum yield for all 5 channels can be measured by probing H and CO above 3F.

Figure 1: 2D REMPI spectra of the CO fragment near threshold for (3), bottom, and above threshold for (5), top. The correlated speed and J distributions for (3), (4) and (5) are obvious, and simple to integrate, providing relative quantum yields for each.


31

Reagent Vibrational Excitation Effect on the Dynamics of the

F+HD Reaction

Xueming Yang

State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China

In the recent years, we have made considerable progresses in the study of the dynamics of the benchmark F + H2 reaction using quantum-state resolved crossed molecular beams scattering method, in combination with accurate quantum dynamics theory. Experimental evidence of reaction resonances, HF (v = 2) forward scattering, has been detected in a full quantum state resolved reactive scattering study of the F + H2 (v = 0) reaction. Highly accurate full quantum scattering theoretical modeling shows that the reaction resonance is caused by two reaction resonance states. This study is a significant step forward in our understanding of dynamical resonances in the benchmark F + H2 system. In addition, we have also studied the F + HD (v = 0) system, this isotope substitution provided an extremely sensitive probe to the reaction resonance potential surface in this system. Further, we have also detected clearly partial wave resolved resonances in the F + HD reaction for the first time. Recently, we have developed an experimental scheme for highly efficient pumping of HD (v = 1) from HD (v = 0) using the stimulated Raman adiabatic passage (SARP) technique. And we have applied this technique to invesitgate the HD reagent vibrational excitation effect on the F + HD reaction. From the state resolved scattering experiment using the D-atom Rydberg tagging technique, we have found that the main reaction product from that F + HD (v = 1) reaction is that HF in the v = 3 state rather than the v = 2 state from the F + HD (v = 0) reaction. This indicates that the reaction is nearly vibrationally adiabatic, in which all excess vibrational energy is deposited to the HF product vibration. State resolved differential cross sections have also been measured, in good agreement with exact quantum calculations based on a newly constructed potential energy surface. Reaction resonances have also been observed in the experiment. A clear resonance picture is also obtained for this F + HD (v = 1) HF + D reaction using the quantum scattering dynamics method.


32

Crossed beam ion imaging study of O(1D) reaction with methane

Yoshihiro Ogi,a) Hiroshi Kohguchi,b) Toshinori Suzuki a,c)

a) RIKEN Center for Advanced Photonics, Japan

b) Department of Chemistry, Graduate School of Science, Hiroshima University, Japan c) Department of Chemistry, Graduate School of Science, Kyoto University, Japan

The scattering distributions of state-selected methyl radicals are measured for the O(1D2) reaction with methane using a crossed molecular beam ion imaging method at collision energies of 0.9 – 6.8 kcal/mol. The results are compared with the reaction with deuterated methane to examine the isotope effects. The scattering distributions exhibit contributions from both the insertion and abstraction pathways respectively on the ground and excited-state potential energy surfaces. Insertion is the main pathway, and it provides a strongly forward-enhanced angular distribution of methyl radicals. Abstraction is a minor pathway, causing backward scattering of methyl radicals with a discrete speed distribution. From the collision energy dependence of the abstraction/insertion ratio, the barrier height for the abstraction pathway is estimated for O(1D2) with CH4 and CD4, respectively. The insertion pathway of the O(1D2) reaction with CH4 has a narrower angular width in the forward scattering and a larger insertion/abstraction ratio than the reaction with CD4, which indicate that the insertion reaction with CH4 has a larger cross section and a shorter reaction time than the reaction with CD4. Additionally, while the insertion reaction with CD4 exhibits strong angular dependence of the CD3 speed distribution, CH3 exhibits considerably smaller dependence. The result suggests that, although intramolecular vibrational redistribution (IVR) within the lifetime of the methanol intermediate is restrictive in both isotopomers, relatively more extensive IVR occurs in CD3OD than CH3OH, presumably due to the higher vibrational state density.

DCSs of CD3 (v = 0, N = 0-2) products observed at Ec of (a) 6.9, (b) 3.9, (c) 1.6, and (d)1.3 kcal/mol.

Left halves: observed 2D projection image. Right halves: slice image of the 3D distribution.

Hot Topic H-07

33

Photoisomerization Action Spectroscopy of

Molecular Ions in the Gas Phase

B. D. Adamson, N. J .A. Coughlan, E. J. Bieske

School of Chemistry, The University of Melbourne, Victoria 3010, Australia A new approach for studying the photoisomerization of molecular ions in the gas phase is described. Packets of molecular ions are injected into a drift tube filled with helium buffer gas, where they are irradiated with tunable laser light. Photoisomerization alters the ions’ cross section for collisions with helium atoms so that they arrive at the ion detector slightly earlier or later than the parent ions. By monitoring the photo-isomer peak as a function of laser wavelength one can record an action spectrum that is related to the ions’ absorption spectrum modulated by the photoisomerization probability. The approach is demonstrated with a series of polymethine dyes including DTC, DTDCI, DODCI and HITC, which undergo trans-cis isomerization about C-C bonds in the polymethine chain that link the equivalent heterocycles.

Arrival time distribution (ATD) for electrosprayed DTC+ cations. Irradiation with light

at 535 nm causes trans–cis isomerization and a modification of the ATD.

As an example, the figure above shows the arrival time distribution of DTC+ cations and the modification resulting from photo excitation at 535 nm, near the peak of the absorption spectrum. Photoisomerization action spectra of the dye cations in the gas phase resemble the corresponding solution phase absorption spectra, but are shifted to shorter wavelength. Aside from providing a means for investigating photo-induced conformational rearrange-ments, the technique may also be applicable to molecular transitions that lead to a long lasting change in a molecule’s multiplicity, thereby changing the effective collision cross section. 1. B.D. Adamson, N.J.A. Coughlan, E.J. Bieske, PCCP, DOI: 10.1039/C3CP51393A.

H-08 Hot Topic

34

A New Type of Vibronic Interactions in the Nitrate Free Radical NO3

Eizi Hirota

The Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan

A new type of vibronic interaction is proposed to replace, to some extent, the traditional explanation made by Neumark and his collaborators1 for the observation of the ν4 progression in the photoelectron spectra of the nitrate anion. Neumark’s interpretation is essentially based upon the Herzberg-Teller (HT) effect between the ground and B excited electronic states, requiring the HT parameter as large as 0.348 eV (2807 cm−1) or 0.290 eV (2339 cm−1). More recently, Stanton2,3 extended Neumark’s approach, based upon an ab initio potential energy surface (PES). He calculated the ν3 fundamental frequency in the ground electronic state to be as low as 1000 cm−1, in sharp contrast with the traditional assignment of the 1492 cm−1 band by Ishiwata, Kawaguchi, et al.4,5 to ν3, and Jacox and Thompson,6 who followed the Stanton proposal, reassigned the 1492 cm−1 band to ν3 + ν4. We (Kawaguchi, Ishiwata, Hirota: KIH) then attempted to detect the A1 + A2 + E components expected for the hot band ν3 + ν4 − ν4 to appear, if Stanton, Jacox, Thompson assignment was correct, thereby eliminating the traditional assignment. However, Hirota7 definitely concluded that only one A – E type component was present in the hot band and this upper A state was not the A sub-state of the ν3 + ν4, but was 2ν2. Hirota7 also found that Stanton’s vibrational anharmonicity constants3 were anomalously large, making expansion of the PES Stanton employed in terms of small-amplitude vibrational coordinates impractical, at sharp variance with the rotational structure of the ν4 fundamental state, which proved to be almost completely free of vibronic perturbations. The 1492 cm−1 band showed two conspicuous anomalies, which were barely encountered in a doubly degenerate band in a non-degenerate electronic state like the A2´ ground-state of NO3. These two were common to other E-type bands. One was the presence of a spin-orbit term and the other the first-order Coriolis coupling constant, of which the observed value differed much from the force-field calculated value. Hirota7 noticed that the effective spin-orbit constant given in the cm−1 unit agreed both in magnitude and sign with the numerical value of the Coriolis coupling constant, and that this fact could be reasonably explained by the close coupling of the vibrational and electronic angular momenta along the symmetry axis. In the ground electronic state the unpaired electron occupies an a2´ orbital, hence no electronic orbital angular momentum is conserved. This situation appears drastically changed, when a doubly degenerate vibraional mode is excited; the angular motion of the unpaired electron about the symmetry axis is modulated by the vibrational mode, introducing some excited electronic state character into the ground electronic state. This new vibronic interaction mechanism will reduce the required HT effect substantially, so that the vibrational and rotational structure in the ground electronic state is not much distorted, as is, in fact, observed in the FTIR spectra.

1. A. Weaver, D. W. Arnold, S. E. Bradforth, D. M. Neumark, J. Chem. Phys. 94, 1740 (1991). 2. J. F. Stanton, J. Chem. Phys. 126, 134309 (2007). 3. J. F. Stanton, Mol. Phys. 107, 1059 (2009). 4. T. Ishiwata, I. Tanaka, K. Kawaguchi, E. Hirota, J. Chem. Phys. 82, 2196 (1985). 5. K. Kawaguchi, E. Hirota, T. Ishiwata, I. Tanaka, J. Chem. Phys. 93, 951 (1990). 6. M. E. Jacox, W. E. Thompson, J. Chem. Phys. 129, 204306 (2008). 7. E. Hirota (to be published).

Hot Topic H-09

35

Rotationally Resolved Spectra of Jahn-Teller Active Free Radicals

Dmitry Melnik,a) Jinjun Liu,b) Terry A. Miller a)

a) Department of Chemistry, The Ohio State University, 100 W. 18th Avenue,

Columbus Ohio, USA b) Department of Chemistry, University of Louisville, Louisville, Kentucky, USA

Conical intersections have become quite important to the study of both the structure and dynamics of molecules. The seminal example of the ramifications of a conical intersection is the Jahn-Teller effect. The Jahn-Teller theorem states that any non-linear polyatomic molecule in a degenerate state will distort to a configuration of lower energy and symmetry. Much work, both theoretical and experimental, has been devoted to understanding the pattern of vibronic levels supported by the Jahn-Teller-distorted potential energy surface. Less attention has been paid to the effect of this distortion on the rotational structure of the molecule even though rotational constants and related molecular parameters are exquisitely sensitive to details of the molecule’s geometry. We have recorded rotationally resolved, jet-cooled, laser-induced-fluorescence spectra of a number of Jahn-Teller active radicals, e.g. methoxy, CH3O, cyclopentadienyl, C5H5, fluoro-benzene cation, C6F6

+, nitrate, NO3, etc. and some pseudo-Jahn-Teller active species, e.g. ethoxy, CH3CH2O, isopropoxy, (CH3)2CHO, methyl-cyclopentadienyl, CH3C5H4, and asymmetrically deuterated derivatives of methoxy and cyclopentadienyl. We have developed new methods for analyzing some of these spectra and the results therefrom will be discussed. Most importantly we consider the implications of these results for characterizing Jahn-Teller-distorted potential energy surfaces, the quenching of spin-orbit coupling, and the effects of weak symmetry breaking by chemical or isotopic substitution.


36

Solid State Pathways towards Molecular Complexity in Space

free radicals @ work

Harold Linnartz

Sackler Laboratory for Astrophysics, Leiden Observatory, PO Box 9513, NL2300 RA Leiden, the Netherlands, www.laboratory-astrophysics.eu

The conditions in space are extreme and not in favor of an efficient chemistry: temperatures are low, radiation fields are intense and particle densities are exceedingly small. Nevertheless, more than 170 different molecular species have been identified in star-forming regions. These comprise both small and complex species as well as stable and transient molecules and are the result of an exotic chemical evolution. Today, astrochemists explain the chemical complexity in space as the cumulative outcome of reactions in the gas phase and on icy dust grains. Gas phase models explain the observed abundances of molecules such as the linear carbon chain radicals C6H and HC11N, but fail to explain the observed abundances of stable species, e.g., water, methanol and acetonitrile (a precursor molecule for the simplest amino acid glycine) as well as larger compounds such as glycolaldehyde, dimethylether and ethyleneglycol. Evidence has been found that these and other complex, organic compounds are made on icy dust grains that act as catalytic sites for molecule formation. It is here that particles ‘meet and greet’ upon (non)energetic processing, such as irradiation by vacuum UV light, interaction with atoms, electrons or cosmic rays, or heating. This contribution reviews the state-of-the-art in solid state astrochemistry. The focus is on laboratory based studies, specifically UV induced processes1,2 and reactions following atom addition reactions.3,4 Related topics – spectral properties, ice porosity, thermal effects, etc. – are shortly addressed as well. The work presented here is discussed along astronomical observations, both of inter- and circumstellar ices and gas phase molecules with a likely solid state origin, and astrochemical models, extending the experimental outcomes onto timescales not accessible in the laboratory. 1. Formation rates of complex organics in UV irradiated CH3OH-rich ices I: Experiments; K.I. Oberg, R.T.

Garrod, E.F. van Dishoeck, H. Linnartz, Astron. Astrophys. 504, 891 (2009). 2. UV photodesorption of interstellar CO ice analogues: from subsurface excitation to surface desorption; M.

Bertin, E.C. Fayolle, C. Romanzin, K.I. Oberg, A. Moudens, L. Philippe, P. Jeseck, X. Michaut, H. Linnartz, J.-H. Fillion, PCCP 14, 9929 (2012).

3. Surface formation routes of interstellar molecules; hydrogenation reactions in simple ices; S. Ioppolo; H.M. Cuppen, H. Linnartz, Red. Fis. Acc. Lincei 22, 211 (2011).

4. Water formation at low temperatures by surface O2 hydrogenation II; the reaction network; H.M. Cuppen, S. Ioppolo, H. Linnartz, PCCP 12, 120 (2010).

Hot Topic H-10

37

Reactivity of Criegee Intermediates CH2OO and CH3CHOO:

Direct Detection and Conformer-Dependent Kinetics

Oliver Welz,a) Arkke J. Eskola,a) John D. Savee,a) Adam M. Scheer,a) Brandon Rotavera,a) David L. Osborn,a) Edmond P. F. Lee,b,c) John M. Dyke,b) Daniel M. K. Mok,c) Carl J.

Percival,d) Dudley E. Shallcross,e) Craig A. Taatjes a)

a) Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94550, USA b) School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK c) Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic

University, Hung Hom, Hong Kong d) School of Earth, Atmospheric and Environmental Sciences, The University of Manchester,

Williamson Building, Oxford Road, Manchester M13 9PL, UK e) School of Chemistry, University of Bristol, Bristol BS8 1TS, UK

Criegee intermediates (C.I.s), carbonyl oxides, have long been implicated as key species in the troposphere. They are formed during the ozonolysis of alkenes, which is a major tropospheric degradation process of these hydrocarbon species. Reactions of C.I.s are thought to contribute to the formation of secondary organic aerosols, OH radicals, and sulfuric acid. Until recently1,2 no gas-phase C.I. had ever been directly observed, nor had the reaction of any C.I. ever been studied in isolation, and indirect determinations of their reactions with key atmospheric species gave rate coefficients spanning orders of magnitude. Here we present the direct detection and measurements of reactions kinetics of the two simplest C.I.s, formaldehyde oxide (CH2OO) and acetaldehyde oxide (CH3CHOO),2,3 in the gas phase at 300 K and 4 Torr. We generated these C.I.s with low internal energies via the reaction of laser-photolytically produced α-iodoalkyl radicals with O2. Time-resolved multiplexed synchrotron photoionization mass spectrometry (MPIMS) allowed the unambiguous identification of CH2OO and CH3CHOO based on their masses, ionization energies, and photoionization spectra. Furthermore, the two distinct conformers of CH3CHOO, syn- and anti-, could be probed independently.3

Both CH2OO and CH3CHOO react far more rapidly with SO2 and with NO2 than models have generally assumed, suggesting a prominent role of C.I.s in tropospheric sulfate chemistry. We show that CH3CHOO displays conformer-dependent reactivity,3 with anti-CH3CHOO substantially more reactive towards H2O and SO2 than is the syn- conformer. These results shed light on the fundamental physical chemistry of Criegee intermediates and help to understand their role in the troposphere. …see also poster A-43 1. C. A. Taatjes, G. Meloni, T. M. Selby, A. J. Trevitt, D. L. Osborn, C. J. Percival, D. E. Shallcross, J. Am.

Chem. Soc. 130, 11883 (2008). 2. O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Percival, D. E. Shallcross, C. A. Taatjes, Science 335,

204 (2012). 3. C. A. Taatjes, O. Welz, A. J. Eskola, J. D. Savee, A. M. Scheer, D. E. Shallcross, B. Rotavera, E. P. F. Lee, J.

M. Dyke, D. K. W. Mok, D. L. Osborn, C. J. Percival, Science 340, 177 (2013).

H-11 Hot Topic

38

Issues of NO Formation in Flames via the NCN Radical Pathway: Rate constants, Absorption Cross Section, and Thermochemistry

G. Friedrichs, J. Dammeier, N. Faßheber

Institute of Physical Chemistry, Kiel University, Max-Eyth-Str. 1, 24118 Kiel, Germany

The generation of prompt-NO by the reaction of small hydrocarbon radicals with atmospheric nitrogen constitutes one of several distinct formation pathways of nitrogen oxides (NOx) in flames. In contrast to textbook knowledge, it has been clearly demonstrated in recent years that the corresponding initiation step CH + N2 does not yield the products HCN + N but H + NCN. Consequently, new submechanisms for NCN chemistry have been implemented into combustion models. As almost no direct measurements on the high temperature reactions of NCN have been available so far, current implementations heavily rely on estimated or theoretically derived rate constant values. Experimental verification mainly originates from NCN detection in flames, which is complicated by low intermediate concentrations and low absorption cross sections. In our pursuit to provide accurate rate constant data for reliable modeling of NCN chemistry, we recently established the thermal decomposition of NCN3 as a clean high temperature radical source. Both 1NCN and 3NCN can be sensitively detected by narrow bandwidth laser absorption at wavelengths around 330 nm allowing us to directly measure the absorption cross section as well as rate constants of NCN reactions behind shock waves. A comprehensive data set on the reactions NCN + H, O, H2, O2, NO, NO2, NCN, M has been assembled that demonstrates a broad spectrum of different kinetic behaviors resulting from unimolecular recombination and rearrangement steps. Despite the substantial experimental, theoretical, and modeling efforts performed by diverse research groups, a consistent modeling of prompt-NO formation in different flames has not been achieved as yet. In particular, a considerable discrepancy of reported values of the high temperature absorption cross section exists, an experimental value of the rate constant of the reaction NCN + OH is still missing, and the channel branching ratio of the reaction NCN + H is uncertain. With CH + N2 or HCN + N as the main products, the latter issue is closely related to the still disputed enthalpy of formation of the NCN radical. The enthalpy of formation needs to be known accurately in order to predict the overall rate constant of the prompt-NO initiation step CH + N2 NCN + H and its reverse reaction, which in turn corresponds to one of the channels of the mentioned NCN + H reaction. The presentation introduces and discusses the results of our direct high temperature measurements in the light of these remaining issues of NCN radical chemistry.

Hot Topic H-12

39

Dimerization of Phenylpropargyl Radicals:

An IR/UV double resonance study

K. H. Fischer,a) J. Hertericha), I. Fischer,a) S. Jaeqxb), A. M. Rijs b,c)

a) Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany

b) FOM institute for plasma physics Rijnhuizen, Edisonbaan 14, 3934 MN Nieuwegein The Netherlands

c) Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 7, 6525 ED Nijmegen,The Netherlands

Although the mechanism of soot formation is not fully understood, there is agreement that C3 hydrocarbons, i.e. molecules with three carbon atoms, play an important role in the generation of aromatic units and the further growths of PAH’s. From three C3-units, the isomers of C9H7 can be formed, resonance-stabilized radicals that can be expected to be rather long-lived and subject to further growth reactions. Their electronic structure has been investigated by Schmidt, Kable and coworkers1. Here we present an IR/UV double resonance spectroscopic study of two C9H7 isomers, 1-phenylpropargyl and 3-phenylpropargyl. The radicals were generated by flash pyrolysis from the corresponding bromides and ionized at 255-297 nm in a one-color two-photon process. Mid-Infrared radiation in the fingerprint region between 500 and 1800 cm-1 was provided by a free electron laser (FEL). It is shown that the two radicals can be distinguished by their infrared spectra. In addition we studied the dimerization products originating from the phenylpropargyl self-reaction. We utilize the fact that the pyrolysis tube can be considered to be a flow reactor, permitting to investigate the chemistry in such a thermal reactor. Dimerization of phenylpropargyl produces predominately species with m/z = 228 and 230. A surprisingly high selectivity has been found: The species with m/z = 230 is identified to be para-terphenyl, while m/z = 228 can be assigned to 1-phenylethynyl-naphthalene. A mass spectrometric investigation aimed at elucidating the role of phenyl in combustion2 revealed strong signals at m/z = 228 and 230, showing the importance of the corresponding molecules in the growth of aromatic systems. Our results allow to derive a mechanism for the dimerization of phenylpropargyl and suggest hitherto unexplored pathways to the formation of soot and PAH. The work has been summarized in a recent publication.3 1 N.J. Reilly, D. L. Kokkin, M. Nakajima, K. Nauta, S. H. Kable, T. W. Schmidt, J. Am. Chem. Soc. 130,

3137 (2008). 2. B. Shukla, M. Koshi, Phys. Chem. Chem. Phys.12, 2427 (2010). 3. K.H. Fischer, J. Herterich, I. Fischer, S. Jaeqx, A.M. Rijs, J. Phys. Chem. A 116, 8515 (2012).


40

Detection of reactive radicals in combustion chemistry

E. Akyildiz,a) T. Bierkandt,a) T. Kasper,a) P. Oßwald,b) M. Köhler,b) P. Hemberger c)

a) Thermodynamics – Institute for Combustion and Gasdynamics, University of Duisburg-

Essen, Lotharstr.1, Duisburg, Germany b) DLR – Institute of Combustion Technology, Pfaffenwaldring 38-40, Stuttgart, Germany

c) Paul Scherrer Institut, Villigen 5232, Switzerland Two of the driving issues of combustion research are the efficiency of combustion processes and emission control. While efficiency is largely determined from the thermochemistry, fluid dynamics and mass or heat transfer of the combustion process, the emissions formed during combustion depend on the chemical kinetics of the process. Combustion intermediates with small concentrations significantly influence the ignition characteristics, inhibition of flames and pollutant formation.1 Many of these reactive flames species are radicals. Some of the radical species are nearly ubiquitous and appear independent of the hydrocarbon fuel being used. Many small radicals such as H, O, OH, HO2, CH, CH2, CH3, C2H3, HCO, CH3O and NO fall into this category. Other radicals are formed during fuel destruction and depend strongly on the molecular structure of the fuel. In flames of chemically pure fuels, the radical species produced by the initial hydrogen abstraction represent the first branching step in the kinetic reaction mechanism. Typically, the branching ratios implemented in reaction mechanisms are investigated in shock tubes or well-defined kinetic experiments with a limited number of species. Comparison of modeled and measured mole fractions for these species in a model flame environment is a very stringent test for model validity. Fuel-H radicals are of special interest because the number of reactions forming these radicals even under flame conditions is limited and deviations can be traced back to individual reactions in the kinetic mechanism. However, the branching ratios of the fuel radicals of larger fuels are notoriously difficult to determine experimentally in flame measurements. Spectroscopic detection schemes of these species are often not well developed and sampling techniques with mass spectrometric or gas chromatographic detection tend to lose too many radicals during transfer from the flame to the detector. Even molecular-beam mass spectrometry coupled with in situ sampling from low-pressure, premixed, flat flames and soft single-photon ionization schemes typically lacks the necessary sensitivity due to sampling losses. In addition, radical signals are often masked by ion fragments with the same mass from dissociative ionization processes of the fuel. In recent measurements at the Swiss Light Source, molecular-beam sampling and single-photon ionization by VUV-synchrotron radiation was followed by detection with an imaging photoion-photoelectron coincidence (iPEPICO) spectrometer. Mass-selected threshold-photoelectron spectra (ms-TPES) allow the discrimination between radical and fragment signals. Because the ms-TPES is like a fingerprint, it offers the option to distinguish between isomers with higher accuracy than overlapping photoionization efficiency curves. Using this technique isomer-resolved concentration profiles could be measured for both fuel-H radicals in a fuel-rich iso-butane flame. Several resonantly stabilized radicals, such as propargyl or allyl radicals, can also be detected as thermal ions when sampling charged species. One of the benefits of the detection of ions is that clogging of sampling probe is less pronounced when sampling from heavily sooting flames. Initial experiments with an newly developed atmospheric pressure ion sampling system show that in the hot exhaust gas of a sooting Bunsen burner flame protonated and non-protonated polyynes as well as PAH ions can be detected with good signal-to-noise ratios. 1. K.C. Smyth, D.R. Crosely, K. Kohse-Höinghaus, J.B. Jeffries (Eds.), Applied Combustion Diagnostics,

Taylor and Francis, 9-33 (2002).


41

Non-adiabatic dynamics in the reaction of O(3P) with propene and propyne

John D. Savee,a) Oliver Welz,a) Sampada Borkar,b) Craig A. Taatjes,a) David L. Osborn a)

a) Combustion Research Facility, Sandia National Laboratories, PO Box 969, Livermore, CA

94551-0969, USA b) Department of Chemistry, University of the Pacific, Stockton, CA 95211, USA

Reactions of O(3P) radicals with unsaturated hydrocarbons are important oxidation processes in combustion chemistry. From a fundamental viewpoint, these reactions are interesting because the initial encounter with closed-shell singlet molecules must occur on a triplet potential energy surface. Nevertheless, a multitude of experiments over several decades have concluded that much of the reactivity happens on the singlet surface, which can only be accessed by intersystem crossing dynamics. Although there have been many detailed studies on the prototypical O(3P) + C2H4 reaction, larger unsaturated hydrocarbons, which have more reactive motifs available, have seen much less investigation. For example, in propene and propyne, the two ends of the double (or triple) bond are distinct, whereas in ethene they are identical. In this work, we use time-resolved Multiplexed Photoionization Mass Spectrometry (MPIMS) to study the mechanism of this reaction. MPIMS provides a global view of the reaction, detecting multiple product channels simultaneously with isomeric specificity. Furthermore, because the reaction takes place in a collisional environment, we can study the competition between stabilization of intermediates compared to bimolecular product channels. We also utilize partially deuterated reactants to gain additional pathway specific information on reactivity. Aided by electronic structure calculations, we assign product channels to spin-allowed and spin-forbidden pathways. These pathway branching ratios can then be used to benchmark theoretical treatments such as non-adiabatic transition state theory and surface hopping trajectory calculations. In this talk we compare and contrast reaction of O(3P) with propene vs. propyne. The results provide insights to the mechanisms and rates of intersystem crossing.

42

-- Notes --

43

Poster Session A On Display: Monday & Tuesday

Attended Time: Monday 19.30 – 22.30

Poster Session A Overview

44

A-01 Carbon clusters and hydrides as free radicals from photolysis of

methane in solid neon M.-Y. Lin, J.-L Lo, H.-C. Lu, S.-H. Chou, Y.-C. Peng, B.-M. Cheng, J. F. Ogilvie A-02 Infrared Absorption of CH3O Radicals Produced upon Photolysis

of CH3ONO in p-H2 matrix Wei-Te Chou, Yu-Fang Lee, Yuan-Pern Lee A-03 High-Resolution Infrared Spectroscopy of Ge2C3 V. Lutter, S. Thorwirth, J. Gauss, T. F. Giesen A-04 Transition State Dynamics of the F + H2O → HF + OH Reaction Rico Otto, Amelia W. Ray, Jennifer Daluz, Robert E. Continetti A-05 The Photodissociation Dynamics of Fulvenallene, C7H6, Investigated by

Velocity Map Imaging J. Giegerich, I. Fischer

A-06 Singlet oxygen O2(a1

g) photogeneration from oxygen encounter complexes X-O2

A.P. Pyryaeva, V.G. Goldort, S.A. Kochubei, A.V. Baklanov A-07 Rotamers of m-chloroanisole studied by two-color resonant two-photon

mass-analyzed threshold ionization spectroscopy Wen Bih Tzeng A-08 Experimental investigations of homogeneous and heterogeneous OH

radical reaction mechanisms F. Goulay, J. Thapa, R. Kumar A.K. A-09 Rotational and Hyperfine Structure in the [17.6]2.5 - X2.5 and [23.5]2.5

- X2.5 Transitions of Iridium Monoxide A. G. Adam, J. A. Daigle, L. M. Esson, A. D. Granger, A. M. Smith, C. Linton, D. W.

Tokaryk, T. C. Steimle A-10 Helium Nanodroplet Isolation Spectroscopy and Ab Initio Calculations of

HO-(O2)n Clusters (n=0-5) Christopher P. Moradi, Tao Liang, Paul L. Raston, Gary E. Douberly A-11 Crossed Molecular Beam Study of the Radical + Radical Reaction N + OH A. Bergeat, P. Casavecchia, F. Leonori, N. Balucani, S. Falcinelli, D. Stranges A-12 Kinetics and Structural Features of Organic Peroxides Supra-molecular

Reactions N. A. Turovskij, Yu.V. Berestneva, E. V. Raksha, E. N. Pasternak A-13 Absorptions Between 3000 and 5500 cm-1 of Normal and Oxygen-18

Enriched cyc-O4+ and cyc-O4

- Trapped in Solid Neon Marilyn E. Jacox and Warren E. Thompson

Overview Poster Session A

45

A-14 Wittig's approach to Landau-Zener made even simpler A. I. Chichinin A-15 Electronic Transitions of Palladium and Vanadium Dimer A. S.-C. Cheung, Yue Qian, Y. W. Ng A-16 Spectroscopic Identification of Dichlorobenzyl Radicals: Substituent

Effect on Electronic Transition Energy Y. W. Yoon, E. H. Lee, S. K. Lee A-17 Ab Initio Studies of Ion-Molecule Reactions Important in the Growth of

Interstellar PAH Cations Samuel A. Abrash, Jordan Akers, Lauren Gallagher, M. Samy El-Shall A-18 Trapping radicals in multishell nanoclusters A. A. Pelmenev, R. E. Boltnev, I. B. Bykhalo, I. N. Krushinskaya, V. V. Khmelenko, D. M.

Lee A-19 Experimental approach for stabilization of free radicals in condensed

helium A. A. Pelmenev, R. E. Boltnev, I. B. Bykhalo, I. N. Krushinskaya, V. V. Khmelenko, D. M.

Lee A-20 Oxygen Atom Recombination in the Presence of Singlet Molecular

Oxygen V. N. Azyazov, A. A. Chukalovsky, K. S. Klopovskiy, D. V. Lopaev, T. V. Rakhimova, M. C.

Heaven

A-21 Novel Radicals prepared by Pyrolysis of Sulfonylazides H. Beckers, X.-Q. Zeng, H. Willner A-22 Far infrared stimulated emission from the E 0g

+ ion-pair state of I2 Shoma Hoshino, Mitsunori Araki, and Koichi Tsukiyama A-23 Ab Initio/RRKM Studies of the Reactions of Dicarbon (C2) with C3H6 and

C4H6 and their Implications in Combustion and Astro-chemistry Alexander Landera, Ralf I. Kaiser, Alexander M. Mebel A-24 Photodissociation of CH3CHO at 248 nm: Overall and Primary Quantum

Yields of CH4, HCO and H Elena Jiménez, Sergio González, Pranay Morajkar, María Antiñolo, Coralie Schoemaecker,

Christa Fittschen, José Albaladejo A-25 Infrared Absorption of Transient Intermediates Observed Using a Step-

Scan Fourier-Transform Spectrometer: the Simplest Criegee Intermediate CH2OO

Yu-Te Su, Yu-Hsuan Huang, Henryk A. Witek, Yuan-Pern Lee

Poster Session A Overview

46

A-26 Spectroscopic properties of the c-C6H7 radical and its cation: a high-level

theoretical study A. Bargholz, R. Oswald, P. Botschwina A-27 Observation of orientation dependent electron transfer in inelastic

molecule-surface collisions Nils Bartels, Kai Golibrzuch, Christof Bartels, Chen Li, Daniel J. Auerbach, Alec M. Wodtke,

Tim Schäfer A-28 Investigation of Combustion Behaviour and Flame Propagation within an

One-Cylinder Internal Combustion Engine A. Thrun, F. Temps

A-29 Rotational Analysis of the A −X System of the C3Ar van der Waals complex

Anthony J. Merer, Yen-Chu Hsu, and Yi-Jen Wang A-30 Vibrational Level Calculations for the Ground Electronic States of C3 and C3Ar Yi-Ren Chen, Anthony J. Merer, and Yen-Chu Hsu A-31 FTMW Spectroscopy and Determination of the 3-D Potential Energy

Surface for Ar–CS C. Niida, M. Nakajima, Y. Sumiyoshi, Y. Ohshima, H. Kohguchi, Y. Endoa) A-32 Jet-cooled excitation spectra of large benzannulated benzyl radicals: 9-

anthracenylmethyl (C15H11) and 1-pyrenylmethyl (C17H11) Gerard D. O’Connor, George B. Bacskay, Gabrielle V.G. Woodhouse, Tyler P. Troy, Klaas

Nauta, Scott H. Kable, Timothy W. Schmidt A-33 Pure beams of chromophore-water clusters: towards the investigation of

the photochemistry of aggregate systems in the molecular frame D. A. Horke, Y.-P. Chang, S. Trippel, T. Mullins, S. Stern, J. Küpper A-34 Conformer-specific reactions with Coulomb-crystallized ions D. Rösch, D. Wild, S. Willitsch, Y.-P. Chang, K. Długołecki, J. Küpper

A-35 Fast 1,2-acyl group migration in the gas phase oxidation of ketone

radicals and their unsaturated hydrocarbon analogs A. M. Scheer, O. Welz, D. L. Osborn, C. A. Taatjes A-36 Laser Induced Inhibition of Cluster Growth (LIICG) -A new method to

measure electronic spectra S. Chakrabartya, M. Holz, A. Banerjee, D. Gerlich, J.P. Maier A-37 Seasonal Measurements of Atmospheric OH Radicals on the West Coast

of Ireland M. Adam, J. McGrath, F. Rohrer, R.L. Mauldin III, B. Bohn, C. Monahan, C.O’Dowd, H.

Berresheim

Overview Poster Session A

47

A-38 Imaging Inelastic Scattering of Methyl Radicals with Gases and Reactive

Scattering of Chlorine Atoms with Propene Thomas J. Preston, Ondrej Tkáč, Greg T. Dunning, Alan G. Sage, Stuart J. Greaves,

Andrew J. Orr-Ewing A-39 Probing the low-temperature chain-branching mechanism for n-butane

autoignition chemistry: Pressure-dependent measurements of ketohydroperoxide formation in pulsed photolytic n-butane oxidation

A. J. Eskola, O. Welz, I. O. Antonov, L. Sheps, J. D. Savee, D. L. Osborn, C. A. Taatjes A-40 Spectroscopy and chemical kinetics of formaldehyde oxide (CH2OO)

using time-resolved broadband cavity-enhanced absorption spectroscopy

Leonid Sheps A-41 Phototautomerization of CH3CHO to CH2=CHOH at Atmospheric Pressure

of N2. Miranda Shaw, Alexander Clubb, Balint Sztaray, David L. Osborn, Meredith J. T. Jordan,

Scott H. Kable A-42 Electronic and Infrared Spectroscopy of Unsaturated Hydrocarbons of

Astrophysical Interest D. Zhao, A. Walsh, K. Doney, M.A. Haddad, W. Ubachs, H. Linnartz A-43 Reactivity of Criegee Intermediates CH2OO and CH3CHOO: Direct

Detection and Conformer-Dependent Kinetics O. Welz, A. J. Eskola, J. D. Savee, A. M. Scheer, B. Rotavera, D. L. Osborn, E. P. F. Lee, J.

M. Dyke, D. M. K. Mok, C. J. Percival, D. E. Shallcross, C. A. Taatjes A-44 FTIR Study of NO3 – Analysis of the 3+ 4 Band and Spin-Orbit Constants

in the Ground 2A2’ State K. Kawaguchi, R. Fujimori, J. Tang, T. Ishiwata

A-01 Poster Session A

48

Carbon clusters and hydrides as free radicals from photolysis

of methane in solid neon

M.-Y. Lin,a) J.-L Lo,a) H.-C. Lu,a) S.-H. Chou,a) Y.-C. Peng,a) B.-M. Cheng,a) J. F. Ogilvie b)

a) National Synchrotron Radiation Research Centre, Hsinchu Science Park, Taiwan

b) Escuela de Quimica and CELEQ, Universidad de Costa Rica As Norman and Porter (1954) originally envisaged, the objective of conducting photochemical experiments within a solid host at a temperature less than 100 K is to trap a free-radical product for leisurely observation, because the host is selected to be chemically inert and because the migration of fragments of photolysis through the solid sample is inhibited.

We report here photochemical experiments on methane, in samples either pure or dispersed in solid neon, in all cases at 3 K, involving irradiation of solid samples in situ with light of wave length tunable in the vacuum-ultraviolet spectral region, generated with an electron synchrotron. The nature of the photochemical products was deduced from their absorption spectra in the mid infrared region, recorded, at each stage of an experiment, with an interferometric spectrometer. The samples varied from pure solid methane to dispersions of methane in solid neon at a nominal ratio Ne : CH4 up to 104. The wavelength of radiation to effect photodecomposition of methane was varied within a range/nm 120 – 165; this radiation is not absorbed by neon, but might be absorbed by methane or any product of its photo-decomposition. The use of methane prepared with isotopic label either 13C or 2H assisted an identification of those products.

If the neon host as dispersant efficiently inhibited migration of other than H atoms through the crystalline lattice, the products detectable with infrared spectra might include CH3, CH2 and CH; we readily identified CH3 and CH and their isotopic variants, but not CH2, as products after an initial brief irradiation of CH4 in Ne. Further irradiation produced lines in the mid infrared spectral region assigned to carbon radical species as clusters from C3 to C14, carbon monohydride radicals from C2H to C5H (the latter not previously characterized experimentally), and other carbon hydrides. A larger ratio of neon to methane facilitated the formation of longer carbon chains. When H2 was added to the neon in a small proportion, such as for samples of composition CH4 : H2 : Ne :: 1 : 6 : 104, the length of the carbon chains of the identified products was extended to C20. These results have no precedent.

Although there was no evidence that the neon dispersant was other than chemically inert in these experiments, a migration by whatever species – likely C or CH or C2 – leading to the formation of carbon radicals as clusters or long chains of C atomic centres, was clearly not effectively inhibited, even at 3 K – well below the standard melting point of Ne at 24.5 K; these radicals, once formed, underwent no further reaction in the absence of ultraviolet radiation.

Infrared and ultraviolet spectra of methane and its photolysis products will be presented, with a suggested mechanism of the photochemical and photophysical processes involving atomic and molecular free radicals.

Poster Session A A-02

49

Infrared Absorption of CH3O Radicals Produced upon Photolysis

of CH3ONO in p-H2 matrix

Wei-Te Chou,a) Yu-Fang Lee,a) and Yuan-Pern Leea, b)

a) Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 1001 Ta-Hsueh Rd., Hinchu 30010, Taiwan

b) Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan The methoxy radical, CH3O, has attracted much attention because of its important molecular structure and also as a reaction intermediate in combustion and atmospheric chemistry.1 CH3O has an electronically degenerate ground state 2E in C3v symmetry and is subject to Jahn-Teller distortion. Its vibrational spectrum is also influenced by spin-orbit splitting (64 cm−1 in the ground vibronic state) due to an unpaired p-orbital electron on the O atom. For rotationally resolved studies of the electronic ground state, previous investigations include laser-induced fluorescence, laser magnetic resonance, and stimulated emission pumping.2–4 High-resolution infrared spectrum of jet-cooled CH3O, produced by laser photolysis of CH3ONO, in the C–H stretching region 2850–2940 cm−1 has been reported.5 However, direct infrared absorption spectrum of CH3O other than the C–H stretching region remains unreported. Irradiation of a p-H2 matrix containing CH3ONO at 3.2 K with light at 355 nm from a Nd:YAG laser produced main features at 1365.4, 1427.5 (21

−, 21+), 1041.8 (31

−), 1346.8, 1427.5, 1520.9, 1520.9 (51

−, 51+, 51

−, 51+), and 689.3/694.9, 945.9/951.7, 1233.5, 1235.9 (61

−, 61

+, 61−, 61

+); labels in parentheses indicate transitions to vibrational states attributable to the umbrella, C–O stretching, CH2 scissoring, and HCO deformation modes of CH3O, respectively. These features appeared upon photolysis and diminished after two minutes; formation of CH2OH was observed as CH3O decayed. The assignments were based on comparison of observed vibrational wavenumbers with those predicted with the quadratic potential energy force field and quadratic dipole moment expansion calculated with the CCSD(T)/cc-pVTZ method.6 Jahn-Teller and anharmonic vibrational contributions were included in the full Hamiltonian to estimate the correlation diagram connecting the harmonic eigenvalues to those of the fully coupled problem. The average deviation between the experimental and the calculated values is 2.7 6 cm 1 with a maximal value less than 12.3 cm−1. The observation of CH3O demonstrates that the cage effect of solid p-H2 is diminished so that isolated CH3O may be produced via UV photodissociation of CH3ONO in situ. This approach provides an excellent method to produce free radicas in solid p-H2. 1. C. R. Kaplan, G. Patnaik, and K. Kailasanath, Combust. Sci. Technol. 131, 39 (1998). 2. S. C. Foster, P. Misra, T.-Y. D. Lin, C. P. Damo, C. C. Carter, and T. A. Miller, J. Phys. Chem. 92, 5914

(1988). 3. D. K. Russell and H. E. Radford, J. Chem. Phys. 72, 2750 (1980). 4. F. Temps, Adv. Ser. Phys. Chem. 4, 375 (1995). 5. J.-X. Han, Y. G. Utkin, H.-B. Chen, L. A. Burns, and R. F. Curl, J. Chem. Phys. 117, 6538 (2009). 6. J. Nagesh and E. L. Sibert III, J. Phys. Chem. A 116, 3846 (2012).


50

High-Resolution Infrared Spectroscopy of Ge2C3

V. Lutter,a) S. Thorwirth,b) J. Gauss,c) T. F. Giesen a)

a) Institut für Physik, Universität Kassel, Heinrich-Plett-Straße40, Kassel, Germany

b )I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, Köln, Germany c )Institut für Physikalische Chemie, Johannes Gutenberg-UniversitätMainz,

Duesbergweg 10-14, Mainz, Germany Gas-phase spectra of molecules and clusters comprising carbon and refractory elements like silicon and germanium are not well studied despite the relevance of these systems in various fields of research such as material sciences, nanotechnology, astrochemistry and theoretical chemistry. Especially for mixed polyatomic germanium-carbon molecules no high-resolution spectroscopic studies have been reported to date. In this contribution, we present the first high-resolution gas-phase measurements of jet-cooled linear Ge2C3 (Ge=C=C=C=Ge). The rovibrational spectrum of the antisymmetric C-C-stretching mode 3 has been observed at 5.2 m and found to exhibit a complex pattern due to the presence of a sizable number of abundant isotopologs. Our study is complemented by high-level quantum-chemical calculations of Ge2C3 at the CCSD(T) level of theory. The data analysis allows for direct comparison of theoretical and experimental results of selected mo-lecular parameters and also permits a comparison of the C-C bond length within the central carbon skeleton of molecules of the general form X2C3 upon terminal substitution with ele-ments such as C, S, Si and Ge.

The figure shows the measured rovibrational spectrum of the recent measurement of Ge2C3.


51

Transition State Dynamics of the F + H2O → HF + OH Reaction

Rico Otto, Amelia W. Ray, Jennifer Daluz and Robert E. Continetti

Department of Chemistry and Biochemistry, University of California, San Diego

9500 Gilman Drive, La Jolla, CA 92093-0340

Progress in understanding the dynamics of gas phase reactions is based on a rigorous comparison between state-to-state experiments on benchmark reactions and high-level dynamical calculations. Although computationally still challenging, a full dimensional quantum mechanical treatment of four-atom reactions on highly accurate PESs is now within reach. An ideal candidate for a four-atom benchmark system is the reaction F + H2O → HF + OH. Experimental studies probing the product state distribution for this system have revealed interesting reaction dynamics, including significant non-adiabatic effects.1 Recently, a full dimensional quantum dynamical treatment of this 19-electron system was carried out,2 providing motivation for further experimental investigation of the reaction dynamics. Anion photodetachment provides an elegant way to initiate the reaction dynamics in the transition state region. Here we present a photoelectron-photofragment coincidence (PPC) study of the dissociative photodetachment of F¯(H2O). Using a photon energy of 4.8 eV (258 nm) the anion is projected onto the neutral reaction surface and the fragments from two different dissociation pathways are collected: a) the higher lying F + H2O + e¯ reactant asymptote and b) the lower energy HF + OH + e¯ product asymptote, as well as stable F(H2O) complexes + e¯. All fragments of this process are detected in coincidence, which allows for a kinematically complete study of the dissociation process. We will show that in the case of F + H2O the PPC method provides an extensive probe of the energy landscape ranging all the way from the reaction barrier down to the loosely bound van-der-Waals complexes. We have also begun to study the effect of selective vibrational excitation on the reaction dynamics by preparing vibrationally excited F¯(H2O) parent anions prior to photodetachment. Initial results for the excitation of the nearly linear ionic F-H-O bond near 2900 cm-1 will be discussed. Vibrationally exciting the parent anions will allow probing of new Franck-Condon regions on the neutral FH2O potential energy surface, providing a more complete picture of the potential energy surface and a new test for dynamical calculations for this reaction. Acknowledgment: This work was funded by the United States Department of Energy, under grant number DE-FG03-98ER14879. 1. A. Zolot, D. Nesbitt, J. Chem. Phys. 129, 184305 (2008). 2. J. Li, R. Dawes, H. Guo, Jour. Chem. Phys. 137, 094304 (2012).


52

The Photodissociation Dynamics of Fulvenallene, C7H6, Investigated by

Velocity Map Imaging

J. Giegerich, I. Fischer

Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland Süd,

Würzburg, Germany Fulvenallene is the most stable C7H6 isomer and is assumed to be an intermediate in the combustion of toluene.1,2 C7H6 has been observed in toluene rich flames and theoretical studies predict it to be the major decomposition product of the benzyl radical.3 It appears that fulvenallene is an important intermediate in oxidation and pyrolysis processes, which are relevant to the combustion of aromatic hydrocarbons and to the formation of PAH.

Fulvenallene was generated from phthalide as a precursor, which decomposes to the reactive intermediate in a vacuum jet flash pyrolysis source. The molecules were excited at around 247 nm. At this wavelength region the excited molecule dissociates to the fulvenallenyl radical C7H5 + H. The H-atom dissociation products were ionized in a [1+1’] REMPI process via the 1s-2p transition. The ionized H-atoms are recorded on a Velocity Map Imaging Detector. The observed translational energy distribution peaks around 0.06 eV. The expectation value for translational energy release lies at around 0.21 eV which accords to ~ 14% of the excess energy. The ionized H-atoms show an isotropic angular distribution, typical for statistical reactions. In addition time-delay scans were carried out. The time-delay scans show a rate with a time constant on the order of 150 ns and are in good agreement with RRKM predictions. The photodissociation dynamics of the precursor, phthalide, was studied, too. 1. M. W. Wong, C. Wentrup, J. Org. Chem. 61, 7022 (1996). 2. N. Hansen, T. Kasper, J. S. Klippenstein, P. R. Westmoreland, M. E. Law, C. A. Taatjes, K. Kohse-

Höinghaus, J. Wang, T. A. Cool, J. Phys. Chem. A 111, 4081 (2007). 3. G. da Silva, J. A. Cole, J. W. Bozzelli, J. Phys. Chem. A 113, 6111 (2009).


53

Singlet oxygen O2(a1

g) photogeneration from oxygen encounter complexes X-O2

A.P. Pyryaeva,a,b), V.G. Goldort,c) S.A. Kochubei,c), A.V. Baklanov,a,b)

a) Institute of Chemical Kinetics and Combustion, Institutskaya Str. 3,

Novosibirsk 630090, Russia b) Novosibirsk State University, Pirogova Str. 2, Novosibirsk 630090, Russia

c) Institute of Semiconductor Physics, Lavrentiev Ave. 13, Novosibirsk 630090, Russia The oxygen molecular environment in gas or condensed phase provides the collision-induced enhancement of UV-radiation absorption by oxygen resulting in dramatic changes of the oxygen photochemistry. This enhancement is governed by encounter complexes X-O2. Recent investigations of the current authors have established that the UV-photoexcitation of oxygen encounter complexes O2-O2 provides a new channel of reactive singlet oxygen species O2(a1

g) formation.1 In present work the main attention is paid to the qualitative and quantitative description of the mechanism of this new photochemical process proceeding via UV-photoexcitation of O2-O2, nitrogen-oxygen N2-O2 and isoprene-oxygen C5H8-O2 encounter complexes in the gas phase. In the experiments gas mixture (pure O2, N2 + O2 or C5H8 + O2) with oxygen elevated pressure up to 150 bar has been excited by laser radiation within and out of the oxygen Wulf-bands 238÷285 nm. Singlet oxygen O2(a1

g) observed and detected by its IR-luminescence centered at 1.27 µm was found to appear via two processes due to absorption by individual O2 molecules and encounter complexes X-O2 respectively. The quantum yield of O2(a1

g) molecules photogenerated by the encounter complexes O2-O2 has been measured in the overall investigated spectral region 238-285 nm and was found to possess rather high maximum value close to 2 at 262.6 nm. The analysis of the colliding O2-O2 pair potential energy surface revealed that oxygen in Herzberg III state O2(A′3 u) photogenerated in the O2-O2 UV-absorption process is assumed to be responsible for singlet oxygen production in the relaxation process O ( ) O ( ) 2 O ( )u g g gA' X a or b3 3 1 1

2 2 2 with further collisional relaxation of b to a state.2 The quantum yield of O2(a1 g) molecules formed by C5H8-O2 encounter complexes has also been measured in present work and the mechanism has been discussed. Singlet oxygen generation is assumed to follow the excitation of any encounter complexes X-O2 in the media (gas or condensed) containing oxygen. Acknowledgment: The authors gratefully acknowledge the financial support of this work by the Russian Foundation for Basic Research (12-03-00170-а).

1. A. P. Trushina, V. G. Goldort, S. A. Kochubei, A. V. Baklanov, Chem. Phys. Letters 485, 11 (2010). 2. A. P. Trushina, V. G. Goldort, S. A. Kochubei, A. V. Baklanov, J. Phys. Chem. A 116, 6621 (2012).


54

Rotamers of m-chloroanisole studied by two-color resonant two-photon

mass-analyzed threshold ionization spectroscopy

Wen Bih Tzeng

Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, 1 Section 4, Roosevelt Road, Taipei 10617, Taiwan. Email: [email protected]

We apply the resonant two-photon ionization (R2PI) and mass-analyzed threshold ionization (MATI) techniques to record the vibronic and cation spectra of m-chloroanisole. The vibronic features appear in two series, built on 35,822 2 and 35,868 2 cm-1, corresponding to the origins of the S1 ← S0 electronic transition (E1’s) of the two rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 67,645 5 and 68,008 5 cm-1 for these two isomeric species. Comparing these data with those of anisole1 and o-chloroanisole,2 we find that the chlorine substitution at the meta position leads to a red shift in the E1 and a blue shift in the IE. The observed R2PI and MATI bands mainly result from the in-plane ring deformation and substituent-sensitive bending vibrations of these species in the electronically excited S1 and cationic ground D0 states.

1. M. Pradhan, C. Li, J.L. Lin, W.B. Tzeng, Chem. Phys. Lett. 407, 100 (2005). 2. H.C. Huang, B.Y. Jin,, W.B. Tzeng, J. Photochem. Photobiol. A 243, 73 (2012).


55

Experimental investigations of homogeneous and heterogeneous OH radical

reaction mechanisms

F. Goulay, J. Thapa, R. Kumar A.K.

Department of Chemistry, West Virginia University, Prospect street, Morgantown, WV USA Elementary chemical reaction mechanisms of OH radicals are investigated both in the gas phase and at the gas-solid interface. Second order thermal rate coefficients for the reaction of OH with aromatic molecules are used to gain information about the reaction entrance channel as well as the structure of the reaction adducts. Heterogeneous mechanisms for the reaction of OH with cellulose surrogates are investigated by detecting the reaction products in the solid phase using NMR spectroscopy. The study of radical reactions with aromatic species using laser spectroscopy is made difficult due to the large absorption cross section of the reactants. In addition, these reactions often proceed by the formation of several long-lifetime adducts in equilibrium with the reactants,1 thus leading to bi- or tri-exponential decay of the OH concentration under pseudo-first order conditions. Global fits of the OH laser-induced fluorescence temporal profiles in the presence of phenyl acetylene and styrene are used to infer the most likely mechanism for these reactions. The heterogeneous reaction of OH radicals with cellulose surrogates such as -methylglucopyranoside and lactose are studied using a quasi-static fixed bed reactor. The solid phase products are detected by electron and nuclear magnetic resonance. The detection of organic radicals in the particles suggests that the reactions proceed via abstraction of a hydrogen from the carbohydrate ring. Further studies will look at the effect of polymerization and substituents on the kinetics and products. This will lead to a better understanding of the oxidation of cellulose during the very early stage of biomass gasification.2 1. Bohn, B.; Zetzsch, C. Phys. Chem. Chem. Phys., 14, 13933-13948 (2012). 2. Mettler, M. S.; Mushrif, S. H.; Paulsen, A. D.; Javadekar, A. D.; Vlachos, D. G.; Dauenhauer, P. J. Energy &

Env. Sci., 5, 5414-5424 (2012).


56

Rotational and Hyperfine Structure in the [17.6]2.5 - X2.5 and

[23.5]2.5 - X2.5 Transitions of Iridium Monoxide

A. G. Adam,a) J. A. Daigle,a) L. M. Esson,a) A. D. Granger,a) A. M. Smith,a) C. Linton,b) D. W. Tokaryk,b) and T. C. Steimle c)

a) Chemistry Department and Centre for Laser, Atomic and Molecular Sciences, University of

New Brunswick, 30 Dineen Dr., Fredericton, NB, Canada E3B 5A3 b) Physics Department and Centre for Laser, Atomic and Molecular Sciences, University of

New Brunswick, 8 Bailey Dr., Fredericton, NB, Canada E3B 5A3 c) Department of Chemistry and Biochemistry, Arizona State University,

Tempe, AZ 85287, USA The laser induced fluorescence spectra of two electronic transitions, [17.6]2.5 - X2.5 and [23.3]2.5 - X2.5, of IrO have been obtained at high resolution using a single mode dye laser to excite IrO molecules in a laser-ablation molecular beam source at the University of New Brunswick (UNB). The UNB spectra had a linewidth of ~180MHz which allowed the measurement of the 193IrO - 191IrO isotope shifts in the rotational lines and established the vibrational assignment of the [23.3]2.5 - X2.5 band as 1 - 0 and confirmed the previous 0 - 0 assignment of the [17.6]2.5 - X2.5 band. Higher J rotational lines in both transitions split into closely spaced doublets resulting from the quadrupole hyperfine structure caused by the I = 3/2 nuclear spin of both Ir isotopes. A rotational analysis of these two bands including the quadrupole hyperfine structure has just been published.1 More recently the [17.6]2.5 - X2.5 transition has been studied using the higher resolution laser-ablation molecular beam apparatus at the Arizona State University (ASU). Linewidths of ~30MHz were obtained which allowed resolution of the magnetic and electric quadrupole hyperfine structure in the low J rotational lines. Results of both the UNB and ASU studies will be presented. A comparison of some of the data is presented in the figure.

Acknowledgment: TCS's contribution was supported by a grant from Fundamental Interactions Branch, Division of Chemical Sciences, Office of Basic Energy Sciences, Department of Energy (DE-FG02-01ER15153-A003). AGA and DWT acknowledge funding from the Natural Sciences and Engineering Research Council of Canada. 1. A. G. Adam, J. A. Daigle, L. M. Esson, A. D. Granger, A. M. Smith, C. Linton, D. W. Tokaryk, J.

Mol.Spectrosc. 286-287, 46-51 (2013).


57

Helium Nanodroplet Isolation Spectroscopy and

Ab Initio Calculations of HO-(O2)n Clusters (n=0-5)

Christopher P. Moradi, Tao Liang, Paul L. Raston, and Gary E. Douberly

Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA The X2Π3/2 hydroxyl (OH) radical has been isolated in superfluid 4He nanodroplets and probed with infrared (IR) laser depletion spectroscopy. From an analysis of the Stark spectrum of the Q(3/2) transition, the -doublet splittings are determined to be 0.198(3) cm-1 and 0.369(2) cm-1 in the ground and first excited vibrational states, respectively. These splittings are 3.6 and 7.2 times larger than their respective gas phase values. A factor of 1.6 increase in the Q(1/2) -doublet splitting was previously reported for the He solvated X2Π1/2

NO radical.1 A simple model is presented that reproduces the observed -doublet splittings in He solvated OH and NO. The model assumes a realistic parity dependence of the rotor’s effective moment of inertia and predicts a factor of 3.6 increase in the OH ground state (J = 3/2) -doubling when the B0

e and B0f rotational constants differ by less than one percent.

We have explored the low temperature chemistry of the hydroxyl radical via in-situ association reactions between OH and other small molecules. For example, the HOOO hydridotrioxygen radical and its deuterated analog (DOOO) have been isolated and spectroscopically characterized following the reaction between OH and O2 within the helium droplets. The IR spectrum in the 3500-3700 cm-1 region reveals bands that are assigned to the

1 (OH stretch) fundamental and 1 + 6 (OH stretch plus torsion) combination band of the trans-HOOO isomer. The helium droplet spectrum is assigned on the basis of a detailed comparison to the IR spectrum of HOOO produced in the gas phase.2 Despite the characteristic low temperature and rapid cooling of helium nanodroplets, there is no evidence for the formation of a weakly bound OH-O2 van der Waals complex, which implies the absence of a kinetically significant barrier in the entrance channel of the reaction. There is also no spectroscopic evidence for the formation of cis-HOOO, which is predicted by theory to be nearly isoenergetic to the trans isomer. Stark spectroscopy of the trans-HOOO species provides vibrationally averaged dipole moment components that qualitatively disagree with predictions obtained from CCSD(T) computations at the equilibrium, planar geometry, indicating a floppy complex undergoing large-amplitude motion about the torsional coordinate. Under conditions that favor the introduction of multiple O2 molecules to the droplets, bands associated with larger H/DOOO-(O2)n clusters are observed shifted ~1-10 cm-1 to the red of the trans-H/DOOO 1 bands. Detailed ab initio calculations are carried out for multiple isomers of cis- and trans-HO3-O2, corresponding to either hydrogen or oxygen bonded van der Waals complexes. Comparisons to theory suggest that the structure of the HO3-O2 complex formed in helium droplets is a hydrogen-bonded 4A species consisting of a trans-HO3 core. The computed binding energy of the complex is approximately 240 cm-1. Despite the weak interaction between trans-HO3 and O2, non-additive red shifts of the OH stretch frequency are observed upon successive solvation by O2 to form the larger clusters with n > 1. 1. K. von Haeften, A. Metzelthin, S. Rudolph, V. Staemmler, and M. Havenith, Phys. Rev. Lett. 95, 215301

(2005). 2. E. L. Derro, T. D. Sechler, C. Murray, and M. I. Lester, J. Chem. Phys. 128, 244313 (2008).


58

Crossed Molecular Beam Study of the Radical + Radical Reaction N + OH

A. Bergeat,a, b) P. Casavecchia,a) F. Leonoria), N. Balucania), S. Falcinellic), D. Strangesd)

a) Dipartimento di Chimica, Università degli Studi di Perugia,

Via Elce di Sotto 8, 06123 Perugia, Italy b) Institut des Sciences Moléculaires, UMR5255 CNRS / Université Bordeaux 1

351 Cours de la Libération, 33405 Talence Cedex, France c)Dipartimento di Ingegneria Civile e Ambientale, Università degli Studi di Perugia

06100 Perugia, Italy d)Dipartimento di Chimica, Università “La Sapienza”, P.le A. Moro 5, Rome I-00185, Italy

The N+OH NO+H reaction and related HNO/HON radicals play an important role in many gas-phase processes, from combustion of N-containing fuels to atmospheric nitrogen-cycle and production of NO in interstellar clouds. Several reactions [H+NO, O+NH], sample the three lowest HNO/HON potential energy surfaces (PESs) (X1A’, a3A” and A1A”), while N(4S)+OH samples only the triplet PES. From a fundamental point of view, N+OH is a prototypical 3-atom radical-radical reaction which has attracted a large theoretical attention over the past decades, and especially in recent years, both at the level of electronic structure calculations of the three lowest PESs and of dynamical calculations (both quasiclassical and quantum) of reactive integral and differential cross sections as well as rate constants on the relevant ab initio PESs1,2,3. The PESs are dominated by deep wells and barrierless reaction pathways. Experimentally, kinetics studies also down to very low (56K) temperatures have been reported recently for N(4S)+OH and the determined rate constants compared with theoretical predictions4. The NO vibrational distribution was determined early on in a flow system by LIF5. However, no experimental scattering studies under single-collision conditions have been reported on this reaction up to date, because of difficulties in generating beams of OH and N radicals sufficiently intense and no scattering calculations have been performed so far on the singlet PESs for the N(2D)+OH reaction. Here, we report on the first determination of the differential cross section for the reaction of both ground state 4S and excited state 2D N-atoms with OH, leading to NO+H. We exploit the capability of generating intense supersonic beams of OH radicals and N(4S, 2D) atoms by radiofrequency discharge in dilute mixtures of H2O and N2 in He, respectively, and a sensitive crossed-beams apparatus with “universal” mass-spectrometric detection and TOF analysis. To overcome interferences from elastically scattered 14N16O impurities (in the reactant beams) we have resorted to using 18OH and 15N, which has allowed us to detect the 15N18O product at m/z=33, a “clean” mass. Product angular distributions have been measured at a collision energy of about 11 kcal/mol. Product velocity distribution measurements are currently under way. The reaction dynamics of the two electronic states of N atoms appear to be distinct. The results are expected to provide a sensitive benchmark for quantum scattering calculations on ab initio triplet and singlet PESs for these “simple”, prototypical radical-radical reactions. Acknowledgments: Support from MIUR (PRIN 2010-2011), EC COST Actions CM0901 “Detailed Chemical Models for Cleaner Combustion” and CM0805 “The Chemical Cosmos: Understanding Chemistry in Astronomical Environments” is gratefully acknowledged.

1. A. Li, C. Xie, D. Xie, H. Guo, J. Chem. Phys. 138, 024308 (2013); and refs. therein. 2. U. Bozkaya, J. M. Turney, Y. Yamaguchi, H. F. Schaefer III, J. Chem. Phys. 136, 164303 (2012). 3. M. Jorfi, P. Honvault, P. Halvick, J. Chem. Phys. 131, 094302 (2009); and refs. therein. 4. J. Daranlot, M. Jorfi, C. Xie, A. Bergeat, M. Costes, P. Caubet, D. Xie, H. Guo, P. Honvault, K. M. Hickson,

Science 334, 1538 (2011). 5. I. W. M. Smith, R. P. Tuckett, C. J. Whitham, J. Chem. Phys. 98, 6267 (1993).


59

Kinetics and Structural Features of Organic Peroxides Supramolecular

Reactions

N. A. Turovskij, Yu.V. Berestneva, E. V. Raksha, E. N. Pasternak

Physical Chemistry Department, Donetsk National University, 24 Universitetskaya Street, Donetsk, 83001 Ukraine

Organic peroxides reactivity causes the elementary stages rate and direction for technologycal processes of organic compounds oxidation, obtaning of new polymer materials. Chemacal activation by quaternary ammonium salts is the perspective method to regulate the reactivity of commercially available organic peroxides. Reaction of organic peroxides and hydroperoxides supramolecular catalytic decomposition in the presence of quaternary ammonium salts includes the stage of ion-molecular reagents recognition. Two-step model for reagent separated ion pairs (Complex ІІ) formation due to peroxide and solvent separated ion pairs interaction is supposed on the base of spectroscopy, kinetics and the molecular modelling data.1,2

ROOR interaction with Q+ CH3CN X (Complex І) is the first stage of the process. The Complex I further reorganozation leads to the reagent separated ion pairs (Complex ІІ) formation. The peroxide bond chemical activation depends on the salt anion and cation nature as well as on solvent molecule. Reaction enthalphies for complexes I and II formation due to peroxide and solvent separated ion pairs interactions as well as reorganization of the Complex I into Complex II were calculated on the results of molecular modelling data.

1. N. A. Turovskij, E.N. Pasternak, E.V. Raksha et al. Oxid. Comm. - 2010. – Vol. 33, No 3. – P. 485 – 501. 2. M. A. Тurovskyj, I. O. Оpeida, O. V. Raksha, O. M. Turovskaya, et al., Order and Disorder in Polymer

Reactivity. Edited by G. E. Zaikov and B. A. Howell New York: Nova Scince Publishers, 2006, pp. 37-51.

Complex ІІ

Q+…CH3CN…X

Complex І

ROOR


60

Absorptions Between 3000 and 5500 cm-1 of Normal and Oxygen-18

Enriched cyc-O4+ and cyc-O4 Trapped in Solid Neon

Marilyn E. Jacox, Warren E. Thompson

Sensor Science Division, National Institute of Standards and Technology

100 Bureau Drive, Gaithersburg, MD 20899-8441, U.S.A. Recently, gas-phase absorptions in the 3000 to 4300 cm-1 spectral region have been assigned1 to combination bands built on ( 1 + 5) of ground-state cyc-O4

+. Other gas-phase experiments2 identified an electronic transition of cyc-O4 complexed with an argon atom between 4000 and 5300 cm-1. Absorptions that correspond closely to these two groups of bands have been observed in neon-matrix experiments in which both cyc-O4

+ and cyc-O4 are trapped in solid neon at 4.3 K. The results will be compared with the gas-phase data, and possible assignments will be considered taking into account the results of isotopic substitution.

1. A. M. Ricks, G. E. Douberly, and M. A. Duncan, Int. J. Mass Spectrom. 283, 69 (2009). 2. J. A. Kelley, W. H. Robertson, and M. A. Johnson, Chem. Phys. Lett. 362, 255 (2002).


61

Wittig's approach to Landau-Zener made even simpler

A. I. Chichinin a,b)

a)Institute of Chemical Kinetics and Combustion, Institutskaya,3, Novosibirsk, 630090 Russia

b) Novosibirsk State University, Pirogova Str.,2, Novosibirsk, 630090 Russia

The Landau-Zener formula was derived in 1932 and since then has remained an important tool in molecular dynamics and spectroscopy. In 2005, C. Wittig proposed a simple derivation of the formula,1 it looks very useful and probably will be widely used. In this note a new derivation of Landau-Zener formula is proposed.2 Several shortcomings of Wittig's derivation are overcome; now it is really "a single line" derivation.

Let there be two nonperturbed diabatic states, labeled 1 and 2, and the energy difference between them is 12 1 2 1 2( ) ( ) ( ) ( ) ,E t E t E t t v F F t where v is velocity, t is time, and

1 1 /F dU dr and 2 2 /F dU dr are the slopes of the potential energy curves. We search for the perturbed wave function in the form 1 2( ) ( , ) ( ) ( , )A t r t B t r t , where 1( , )r t and

2 ( , )r t are eigen functions of the nonperturbed Hamiltonian. The perturbation is given by time-independent off-diagonal matrix elements 12H , and 12 12| |H . Putting the wave function into the time-dependent Schrödinger equation yields the differential equation 2

12( ) ( ) ( ) 0B t i tB t B t , (1) where B is a complex function, and all other parameters are real. We assume that | ( ) | 1B and the aim is to find | ( ) | fB B . After dividing (1) by tB and integrating over t one

obtains: 212ln ( / ) (1/ ) ( / ) / /f xB B B dt i B B t dt I i⎡ ⎤⎣ ⎦∫ ∫ , (2)

here the integral at the right side is denoted as xI . From Eq. (1) it follows that the expression in square brackets has no pole at 0t . The xI integral may be calculated from the relation 0x CI I , where CI is the contour integral, see figure. The CI integral may be obtained from integral of Eq. (2) by replacing real t by complex variable | | iz z e ( | |z ):

212 ( ) / ( ) /CI B z B z z dz⎡ ⎤⎣ ⎦∫ 2

12 | |0( / ) zi B B d∫ 2

12i , (3)

where the upper and the lower sign correspond to semicircle in upper and lower part of the complex plane, respectively. According to Eq. (1), 2

| |( / ) ~zB B z , hence this term vanishes. Substituting the result from Eq. (3) in Eq. (2) gives 2

12exp( / )fB . Since B is a wave function coefficient, it should be | | 1B ; this condition makes one of the signs impossible. Finally, we obtain the Landau-Zener formula for the probability of nonadiabatic transition: 2 2 2 2

12 12 1 2| | exp( 2 / | |) exp( 2 / | |)LZ fP B v F F . 1. C. Wittig, J. Phys. Chem. B, 109, 8428 (2005). 2. A. I. Chichinin, J. Phys. Chem. B, 117, 6018 (2013).

Ix tIC


62

Electronic Transitions of Palladium and Vanadium Dimer

A. S.-C. Cheung, Yue Qian, Y. W. Ng

Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong

Electronic transition spectra of palladium dimer (Pd2) and vanadium dimer (V2) in the visible region between 480 nm to 700 nm have been studied. Gas-phase Pd2 and V2 molecules were produced by laser ablation of palladium and vanadium metal rods respectively with argon as carrier gas and their laser induced fluorescence (LIF) spectra have been recorded and analyzed. For the Pd2 molecule1

, eleven vibrational bands have been observed and assigned to have v = 0 – 3 and v = 0 – 1 for the [17.1]3Πg – X3Σu

+ system. It is because the palladium metal has five isotopes with appreciable abundance; all vibrational bands observed for Pd2 show no resolved rotational structure. In our analysis, all vibrational bands observed are transitions with = 1. For the ground X3Σu

+ and the [17.1]3Πg states, the bond length and G½ were determined to be 2.47 Å and 2.53 Å, and 211.38 and 218.13 cm-1, respectively. The splitting of the ground state X3Σu

+ has been observed; a weak transition with 3Π0 – X3Σ0+ indicates the

spin-orbit splitting of the ground X3Σu+ state is about 7.9 cm-1 which is close to the theoretical

value of 9 cm-1 from ab initio calculations. Other computational results obtained for the ground X3Σu

+ state are also compared in this work. For the V2 molecule2, six vibrational bands were assigned to a new C3Σu

- – X3Σg- transition

system. The vibrational bands obtained are transitions with = 0. From the analysis of rotationally resolved LIF spectra, the rotational constant for the ground X3Σg

- and C3Σu- states

were determined to be B0 (0g+) = 0.2097 cm-1 and B0 (0g

+) = 0.1609 cm-1, which corresponds to a bond length of r0 = 1.777 Å and r0 = 2.029 Å, respectively. The G½ separation for the C3Σu

- (0g+) is 393.04 cm-1.

A molecular orbital energy level diagram has been used to understand the electronic structure of Pd2 and V2 molecules as well as the nickel-group and vanadium-group of dimers. A discussion of the chemical bonding of these transition metal dimers will also be presented in this work.

1. Joe Ho, K.M. Ervin, M. L. Polak, M.K. Gillies and W. C. Lineberger, J. Chem. Phys. 95, 4845 (1991). 2. P.R.R. Langridge-Smith, M.D. Morse, G.P. Hansen, R.E. Smalley, A.J. Merer, J. Chem. Phys. 80, 593

(1984).


63

Spectroscopic Identification of Dichlorobenzyl Radicals:

Substituent Effect on Electronic Transition Energy

Y. W. Yoon, E. H. Lee, S. K. Lee

Department of Chemistry, Pusan National University, Jangjeong-dong,Geumjung-gu, Pusan 609-735, Republic of Korea

Although the benzyl radical, a prototype of aromatic free radical and reaction intermediate in aromatic chain reactions, has been the subject of numerous spectroscopic studies, chloro-substituted benzyl radicals have received less attention, due to the difficulties associated with production of radicals from precursors.1

The vibronically excited but jet-cooled dichlorobenzyl radicals were generated by the corona discharge of dichlorotoluenes in a technique of corona excited supersonic expansion (CESE) using a pinhole-type glass nozzle developed in this laboratory, from which vibronic emission spectra were observed with a long-path double monochromator in the visible region. The emission spectra show very weak intensity due to the existence of Cl atoms in the precursor molecules and possible breakdown of benzene ring by free Cl atoms in the gas medium. Nevertheless, we could clearly identify the origin band and several well-known vibrational modes from the analysis of the spectra observed.2 In addition, we found that the origin bands of the dichlorobenzyl radicals in the D1 → D0 transition, as listed in Table 1, exhibit the shift to red region compared to the parental benzyl radical at 22002 cm-1, suggesting the lowering energy of the excited electronic state by substitution of Cl atoms into benzene ring. The shifts of the origin bands of bi-substituted benzyl radicals are expected to be larger than those of mono-substituted ones due to the further increase of the space available for delocalized π electrons on the benzene ring and are qualitatively predictable by simply summing up the contribution of each substituent already determined from chlorobenzyl radicals. Recently, we discovered that the substituent effect on the electronic transition energy of the substituted benzyl radicals is associated with the symmetry of electronic states as well as the orientation of substituents on the benzene ring plane at given electronic states.

In this presentation, we are willing to report the relevance3 of the model developed from Hückel’s molecular orbital theory to explain the shift of the electronic transition energy at a given electronic state as well as the spectroscopic observation of jet-cooled dichlorobenzyl radicals using the technique of CESE coupled with a pinhole-type glass nozzle developed in this laboratory for laser-free spectroscopy of transient species. 1. Y. W. Yoon, S. K. Lee, J. Chem. Phys. 136, 024309 (2012). 2. Y. W. Yoon, C. S. Huh, S. K. Lee, Chem. Phys. Lett, 550, 58 (2012). 3. C. S. Huh, Y. W. Yoon, S. K. Lee, J. Chem. Phys. 136, 174306 (2012).

Table 1: Observed data of dichlorobenzyl radicals Cl positions Origin band (cm-1) Shift (cm-1)

2,6- 20153 1849 3,5- n/a n/a 2,3- 20434 1568 2,4- 20980 1022 2,5- 19984 2018 3,4- 21098 904


64

Ab Initio Studies of Ion-Molecule Reactions Important in the Growth of

Interstellar PAH Cations

Samuel A. Abrash,a) Jordan Akers,a) Lauren Gallagher a) and M. Samy El-Shall b)

a) Department of Chemistry, University of Richmond, 28 Westhampton Way, Richmond, VA, USA

b) Department of Chemistry, Virginia Commonwealth University, 1001 West Main Street, Richmond, VA, USA

The molecular carriers of the Diffuse Interstellar Bands (DIBs) remain a mystery to this day. Recent attention has been paid to the possibility that the carriers for these spectral features may derive from cations of polycyclic aromatic hydrocarbons (PAHs). However, the mechanisms by which these large molecules form in the diffuse, cold and hostile environment of interstellar space are not yet well understood. We report on ab initio and density functional studies of ion-molecule reactions, and ion-molecule complex formations that are relevant to the growth of these large molecules from the small molecule building blocks known to be plentiful in space.


65

Trapping radicals in multishell nanoclusters

A. A. Pelmenev,a) R. E. Boltnev,a) I. B. Bykhalo,a) I. N. Krushinskaya,a)

V. V. Khmelenko,b) D. M. Leeb)

a) Branch of Talrose Institute for Energy Problems of Chemical Physics RAS, Chernogolovka, 142432, Russia

b) Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA

Advantages of an experimental techique for the stabilization of free radicals in multishell nanoclusters are discussed. An injection technique in which an impurity-helium gas jet passed through a radiofrequency discharge into a volume of superfluid helium (HeII) was developed in the early 1970’s.1 During cooling of the helium jet from 80-100 K down to 1.5 K, the impurity particles form clusters. Due to the higher polarizability the heavier impurity particles formed the cores of the clusters. The lighter impurities adsorbed at lower temperatures and formed shells surrounding a core. The outer shell of such cluster consists of helium atoms (1-2 layers). Shells of solid helium prevented a coalescence of neighboring clusters and recombination of radicals. Adding a heavier impurity greatly enhanced the stabilization efficiency of radicals.2 ESR spectroscopy studies of H atoms in clusters prepared by condensation of a H2-Kr-He gas mixture had revealed different trapping sites of hydrogen atoms inside krypton cores and inside the molecular hydrogen films.3 Localization of radicals on the clusters’ surfaces allows storage of very high concentrations of radicals. Local densities of nitrogen atoms up to 2 1021 cm-3 were detected in nitrogen-krypton clusters.4 Luminescence spectra of excited nitrogen particles in clusters prepared by condensation of N2-Ne-He gas mixture gave evidence of sublimation of neon shells at 8 K during warm-up. Before the neon sublimation the luminescence spectra corresponded to nitrogen species trapped in a neon matrix, but after the neon sublimation, we observed the spectra of nitrogen species trapped in a molecular nitrogen matrix.5 Experimental capabilities of this experimental techique may be extended by co-condensation of other impurity particles carried by second jet crossing a “hot” jet passed through a radiofrequency discharge. Different kinds of radicals can be stabilized in this way in multishell nanoclusters. The method is also very promising for studying gas phase reactions at low temperatures. Luminescence spectra of KrD* molecules were detected by crossing a “hot” Kr-He jet with a “cold” D2-He jet. 1. E. B.Gordon, L. P. Mezhov-Deglin, O. F. Pugachev, JETP Lett. 19, 103 (1974). 2. R. E. Boltnev, E. P. Bernard, J. Jarvinen, I. N. Krushinskaya, V. V. Khmelenko, D. M. Lee, J. Low Temp.

Phys. 158, 468 (2010). 3. R.E. Boltnev, J. Jarvinen, E.P. Bernard, V.V. Khmelenko, and D.M. Lee, Phys. Rev. B 79, 180506(R) (2009). 4. S. Mao, R. E. Boltnev, V. V. Khmelenko and D. M. Lee, Low Temp. Phys. 38, 1313 (2012). 5. V.V. Khmelenko, A.A. Pelmenev, I.N. Krushinskaya, I.B. Bykhalo, R.E. Boltnev, and D.M. Lee, J. Low

Temp. Phys. 171, 302 (2013).


66

Experimental approach for stabilization of free radicals

in condensed helium

A. A. Pelmenev,a) R. E. Boltnev,a) I. B. Bykhalo,a) I. N. Krushinskaya,a) V. V. Khmelenko,b) D. M. Leeb)

a) Branch of Talrose Institute for Energy Problems of Chemical Physics RAS,

Chernogolovka, 142432, Russia b) Department of Physics and Astronomy, Texas A&M University,

College Station, TX 77843, USA We present our latest results on the stabilization of free radicals in condensed helium. An injection technique involving an impurity-helium gas jet passed through a radiofrequency discharge into a volume of superfluid helium (HeII) was developed in the early 1970’s.1 Upon cooling the helium jet from 80-100 K down to 1.5 K, the impurity particles formed clusters. Solid helium (1-2 layers) adsorbed on the clusters’ surfaces prevented their coalescence. The impurity nanoclusters (with the characteristic diameter of 4-6 nm) formed impurity-helium condensates (IHCs) in the HeII bulk. IHCs are porous materials with very low impurity density (~1020 cm−3).2 High average concentrations of stabilized free radicals (~1019 cm-3) can be achieved on the large total surface (~100 m2/cm3) of impurity nanoclusters. Some different modifications of the injection technique will be presented in our report. ESR studies of radicals gave evidence for tunneling reactions3 and detected very high local concentrations (~1021 cm-3) of stabilized radicals.4 X-ray diffraction studies had revealed structural transformations of impurity clusters upon warm-up.5 Warming of the IHCs leads to the evaporation of helium atoms adsorbed on the impurity nanocluster surfaces. That is a trigger mechanism for destruction of impurity-helium condensates and initiation of free radical recombination and formation of excited atoms and molecules observed by means of optical spectroscopy.6

1. E. B.Gordon, L. P. Mezhov-Deglin, O. F. Pugachev, JETP Lett. 19, 103 (1974). 2. V. Kiryukhin, E. P. Bernard, V. V. Khmelenko, R. E. Boltnev, N. V. Krainyukova and D. M. Lee, Phys. Rev.

Lett. 98, 195506 (2007). 3. V. V. Khmelenko, E. P. Bernard, S. А. Vasiliev, D. M. Lee, Russ. Chem. Rev. 76, 1107 (2007). 4. S. Mao, R. E. Boltnev, V. V. Khmelenko and D. M. Lee, Low Temp. Phys. 38, 1313 (2012). 5. N. V. Krainyukova, R. E. Boltnev, E. P. Bernard, V. V. Khmelenko, D. M. Lee, and V. Kiryukhin, Phys.

Rev. Lett. 109, 245505 (2012). 6. V. V. Khmelenko, I. N. Krushinskaya, R. E. Boltnev, I. B. Bykhalo, A. A. Pelmenev, and D. M. Lee, Low

Temp. Phys. 38, 871 (2012).


67

Oxygen Atom Recombination in the Presence of Singlet Molecular Oxygen

V. N. Azyazov,a) A. A. Chukalovsky, b) K. S. Klopovskiy,b) D. V. Lopaev,b)

T. V. Rakhimova,b) and M. C. Heaven c)

a) P.N. Lebedev Physical Institute, Samara Branch, Samara, 443011, Russia b) Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow 119992, Russia

c) Department of Chemistry, Emory University, Atlanta, GA 30322, USA Active O2 and O3 molecules have an appreciable impact on atmospheric chemistry1

. A

vibrationally excited ozone molecule O3(υ) formed in the recombination process

O(3P) + O2(X3 ) + M O3(υ) + M (1)

either stabilizes via VV, VT and radiative processes or reacts with the atmospheric active species. Recently the rapid quenching of singlet oxygen O2(a1 ) in O(3P)/O2/O3 system had been observed in the laboratory studies2,3. They also observed that the rate of O(3P) removal in the recombination process (1) was lower than predicted. It was supposed that O2(a1 ) is rapidly quenched by vibrationally excited ozone in the process

O2(a1 ) + O3(υ) O(3P) + 2 O2 (2)

to explain both observed phenomena. In this work additional experimental evidence arguing for mechanism where vibrationally excited ozone is an important O2(a1 ) quenching agent in O(3P)/O2/O3 systems have been obtained. Quenching of O2(a1 ) in O(3P)/O2/O3 mixtures had been observed using 248 nm laser photolysis of ozone to produce oxygen atoms and singlet oxygen O2(a1 ) molecules. The kinetics of O2(a1 ) quenching were followed by observing the 1268 nm fluorescence of the O2 a1 → X3 transition. The temporal profiles of the oxygen atom concentrations were monitored by means of the O + NO + M chemiluminescent reaction. It was found that the rate O(3P) removal in the recombination process in our experimental conditions was only half that recommended, indicating the possibility of O(3P) regeneration in the presence of O2(a1 ) in the process (2). Analysis of experimental data shown that vibrationally excited ozone is an important O2(a1 ) quenching agent in O(3P)/O2/O3 systems. At the attitudes near to 90 km the rate of O2(a1 ) removal in the process (2) is compared with that of its quenching by molecular oxygen in the process

O2(a1 ) + O2(X3 ) O2(X3 ) + O2(X3 ). (3)

The contribution of the process (2) on the O(3P), O2(a1 ) and O3 budgets in the middle atmosphere and oxygen-containing plasma is discussed. 1. T.G. Slanger, Science, 265, 1817 (1994). 2. V.N. Azyazov, P.A. Mikheyev, D. Postell, M.C. Heaven, Chem. Phys. Lett., 482, 56 (2009). 3. A.N. Vasiljeva, K.S. Klopovskiy, A.S. Kovalev, D.V. Lopaev, Y.A. Mankelevich, N.A. Popov, A.T.

Rakhimov, T.V. Rakhimova, J. Phys. D: Appl. Phys., 37, 2455 (2004).


68

Novel Radicals prepared by Pyrolysis of Sulfonylazides

H. Beckers, X.-Q. Zeng, H. Willner

FB C-Anorganische Chemie, Bergische Universität Wuppertal,

Gaussstrasse 20, Wuppertal, Germany Flash vacuum pyrolysis (FVP, 800°C) of FSO2N3 produced the thermally persistent triplet fluoro sulfonyl nitrene, FSO2N, in yields up to 66 % (Eq.1).1 Its lifetime in the gas phase was found to be dominated by a precursor concentration dependent triplet nitrene dimerisation. This reaction finally gave access to the elusive fluoro sulfonyl radical, FSO2 (Eq2).1 FSO2N3 → FSO2N + N2 (1) 2 FSO2N → 2 FSO2 + N2 (2) To the contrary, FVP of F3CSO2N, highly diluted in Ar, yields the novel planar iminyl radical O2SN.2 The favorable formation of O2SN according to Eq. (3) and (4) is consistent with the low bond dissociation energy of 66 kJ mol-1 predicted by CBS-QB3 calculations for the F3C + S + bond in the singlet F3CSO2N nitrene intermediate. F3CSO2N3 → F3CSO2N + N2 (3) F3CSO2N → O2SN + CF3 (4)

The pyrolysis products were deposited with an excess of noble gases (Ne, Ar, 1:500) as solid cryogenic matrices (< 20 K), and the novel radicals were fully characterized by their IR and UV/Vis spectra guided by quantum chemical calculations, as well as by their photochemistry. 1. X.-Q. Zeng, H. Beckers, H. Willner, J. Am. Chem. Soc. 135, 2096 (2013). 2. X.-Q. Zeng, H. Beckers, H. Willner, Angew. Chem. submitted (2013).


69

Far infrared stimulated emission from the E 0g

+ ion-pair state of I2

Shoma Hoshino, Mitsunori Araki, and Koichi Tsukiyama

Graduate School of Chemical Sciences and Technology, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 162-8601, Japan

Amplified spontaneous emission (ASE) is radiation initially triggered by spontaneous emission and then amplified by stimulated emission as it passes through a medium having a population inversion. Recently we reported infrared ASE from the f 0g

+ ion-pair state of I2.1 In the current work, we present the first direct detection of stimulated emission in the far infrared (FIR) spectral region from the E 0g

+ ion-pair state of I2.

The E 0g+ ion-pair state was excited via the B 0u

+

(υB = 19) valence state by using an optical-optical double resonance technique. The FIR stimulated emission and UV fluorescence was detected on and perpendicular to the laser propagation direction, respectively.

The strong UV fluorescence assignable to the D 0u

+ (υD = 0) → X 0g

+ state was observed when the E 0g

+ (υE = 0) state was excited (Fig. 1a,

lower panel). The population in the D 0u+ state

was believed to be transferred from the laser prepared E 0g

+ state mainly through the stimulated emission. In fact, as shown in Fig. 2, we succeeded to observe FIR radiation around 26 μm corresponding to the P- as well as R-branch belonging to the E 0g

+ (υE = 0) → D 0u

+ (υD = 0) transition. On the other hand, the

UV fluorescence from the D 0u+ state consists

not only of the strong υD = 0 component but also of the weak υD = 1, 2, and 3 components. We measured the pressure dependence of the UV fluorescence intensities with Ar gas. With increasing pressure the UV fluorescence from the υD = 0 level decreased rapidly, while that from the υD = 1, 2, and 3 levels exhibited no considerable change. Accordingly, we concluded that the two independent decay channels operated for the formation of the D 0u

+

state from the E 0g+ state: FIR stimulated

emission process and the collisional transfer for the production of υD = 0 and υD = 1, 2, and 3, respectively.

1. Hoshino et al., J. Chem. Phys. 138, 104316 (2013).

300 350 400 450

Pure I2 (26 Pa)

I2 + Ar (7.0 x 102 Pa)

D' → A' → A

(b)

(a)D → a'

E → C(B'')

E → A

D → 0g+(ab)

E → BD → X

Em

issi

on in

tens

ity (a

rb. u

nits

)

Wavelength (nm)

24 25 26 27 28

vE = 0 → v

D = 0

P52

R50

Em

issi

on in

tens

ity (a

rb. u

nits

)

Wavelength ( m)

Fig. 1. The dispersed fluorescence spectrum obtained upon the excitation of the E 0g

+ (υE = 0) state at (a) 26 Pa and (b) 7.0 × 102 Pa.

Fig. 2. The dispersed FIR stimulated emission spectrum from the υE = 0 level of the E 0g

+ state.


70

Ab Initio/RRKM Studies of the Reactions of Dicarbon (C2) with C3H6 and

C4H6 and their Implications in Combustion and Astrochemistry

Alexander Landera,a) Ralf I. Kaiser,b) Alexander M. Mebel a)

a) Department of Chemistry and Biochemistry, Florida International University

11200 SW 8th Street, Miami, FL 33199, USA b) Department of Chemistry, University of Hawai’i at Manoa, Honolulu, HI 96822, USA

Formation mechanisms of polycyclic aromatic hydrocarbons (PAH), which are toxic byproducts formed during the incomplete combustion of fossil and bio fuel and are considered as potent atmospheric pollutants due to their carcinogenic and mutagenic character and also may play the critical role in soot growth and in the formation of nanometer sized carbonaceous dust particles in the outflow of circumstellar envelopes, often involve reactions of resonantly stabilized free radicals (RSFRs) and aromatic radicals (ARs). In RSFRs such as propargyl C3H3, 1,2,3-butatrien-1-yl i-C4H3, and cyclopentadienyl C5H5, the unpaired electron is delocalized and spread out over two or more sites in the molecule. This results in a number of resonant electronic structures of comparable importance. Owing to the delocalization, resonantly stabilized free hydrocarbon radicals are, similar to aromatic radicals such as phenyl, more stable than ordinary radicals. Consequently, RSFRs and ARs can reach high concentrations in flames and these high concentrations make them important reactants to be involved in the formation of PAH. Hence, it is important to comprehend how RSFRs and ARs themselves can be produced. In recent years, we investigated theoretically a number of reactions of atomic carbon C(3P) and a dicarbon molecule C2(X1Σg

+/a3Πu) with unsaturated hydrocarbons leading to the formation of RSFRs and ARs, in conjunction with crossed molecular beam experimental studies.

In this work, we present results of CCSD(T)/CBS//B3LYP ab initio calculations of potential energy surfaces for the reactions of singlet and triplet C2 with propene and C4H6 isomers. These calculations are combined with RRKM calculations of reaction rate constants utilized to predict product branching ratios depending on the collision energy under single-collision conditions. The reactions proceed by barrierless addition of C2 to C3H6 or C4H6 followed by isomerizations on the C5H6 and C6H6 surfaces, respectively, and dissociation via H or CH3 eliminations. Routes leading to the formation of the cyclic cyclopentadienyl (C5H5) and phenyl (C6H5) radicals and their chain isomers are overviewed and the results are compared to the recent experiments in crossed molecular beams.

In particular, our results show that the reaction of dicarbon with 1,3-butadiene predominantly forms the aromatic phenyl radical on the triplet surface, whereas the thermodynamically less stable acyclic H2CCHCCCCH2 isomer is mostly produced on the singlet surface. The reactions of C2 with the other C4H6 isomers, 1,2-butadiene and 1- and 2-butynes, lead to the formation of acyclic C6H5 isomers with a minor yield of phenyl. The reaction of C2 with C3H6 is found to produce two RSFRs, 1-vinylpropargyl and 1-methylbutatrienyl + H, as well as i-C4H3 + CH3. A comparison of the theoretically computed branching ratios and experimentally measured relative yields of the products formed by H loss from the methyl and vinyl groups of propene allowed us to evaluate, for the first time, the ratio of singlet and triplet dicarbon molecules present in the experimental beam and reacting with C3H6.


71

Photodissociation of CH3CHO at 248 nm: Overall and Primary Quantum

Yields of CH4, HCO and H

Elena Jiméneza,b), Sergio Gonzáleza), Pranay Morajkarc), María Antiñoloa), Coralie Schoemaeckerc), Christa Fittschenc) and José Albaladejo a,b)

a) Departamento de Química Física Universidad de Castilla-La Mancha. Facultad de Ciencias y Tecnologías Químicas. Edificio Marie Curie. Ciudad Real, 13071 Spain

b) Instituto de Combustión y Contaminación Atmosférica. Universidad de Castilla-La Mancha. Camino de Moledores s/n. Ciudad Real, 13071 Spain

c) Université Lille Nord de France, Laboratoire PC2A - UMR CNRS 8522, Cité Scientifique, Bât. C11, 59655 Villeneuve d’Ascq, France

The primary photodecomposition of CH3CHO has been the subject of many experimental and theoretical studies. Recently, Calvert et al.1 have reviewed the studies on the photochemistry of this aldehyde which can occur by the following pathways:

CH3CHO + h CH3 + HCO (1a) CH4 + CO (1b) CH3CO + H (1c) CH2CO + H2 (1d)

The radical forming channels (1a and 1c) are endothermic ( Hº298K, are 355.3 and 373.5 kJ mol-1, respectively) and the molecular channel (1b) is exothermic and accessible to all wavelengths ( Hº298 = - 19.5 kJ mol-1). Channel (1d) is thermodynamically favored, however Moortgat et al.2 concluded from an absence of any H2 as photolysis product an upper limit of

1d 0.01 at wavelengths >290nm.

To our knowledge, no quantum yield measurements on CH3CHO were reported in the literature at 248 nm. Therefore, in this work the pulsed laser photolysis of CH3CHO/ O2 mixtures at 248 nm was investigated to determine the overall photodissociation quantum yield of acetaldehye and the primary products (CH4, H and HCO). Direct quantification of CH3CHO and CH4 was performed by Fourier transform infrared spectroscopy at 298 K as a function of total pressure (100-760 Torr). The procedure to determine the photolysis quantum yields was the same as previously described by Antiñolo et al.3,4 in the photolysis of fluorinated aldehydes at 308 nm. In the presence of O2 added, indirect measurements of HCO radicals and H atoms were carried out by monitoring HO2 radicals by cw-cavity ringdown spectroscopy at 50 Torr of He.5

Based on the measured quantum yields molecular channel forming CO and CH4 seems to be the main photodissociation (74% of the overall loss of CH3CHO), pathway at 248 nm. 1. J. G. Calvert, R. G. Derwent, J. J Orlando, G. S. Tyndall, T. J. Wallington. Mechanisms of Atmospheric

Oxidation of the Alkanes, Ed. Oxford University Press. (2008). 2. G. K. Moortgat, H. Meyrahn, P. Warneck. Chem. Phys. Chem, 11, 3896 (2010). 3. M. Antiñolo, E. Jiménez, J. Albaladejo, Phys. Chem. Chem. Phys. 13, 15936 (2011). 4. M. Antiñolo, E. Jiménez, J. Albaladejo, J. Photochem. Photobiol. A: Chem. 231, 33 (2012). 5. Parker; C. Jain; C. Schoemaecker; P. Szriftgiser; O. Votava; C. Fittschen. Appl. Phys. B: Lasers and Optics

103 (2011) 725.


72

Infrared Absorption of Transient Intermediates

Observed Using a Step-Scan Fourier-Transform Spectrometer: the Simplest Criegee Intermediate CH2OO

Yu-Te Su,a) Yu-Hsuan Huang,a) Henryk A. Witek,a) Yuan-Pern Lee a,b)

a) Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung

University, 1001, Ta-Hsueh Road, Hsinchu 30010, Taiwan b) Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan

We employed the time-resolved Fourier-transform infrared absorption spectroscopy to investigate IR absorption of unstable gaseous species. A flow reactor (White cell) with optics for a multipassing IR probe beam was coupled to a step-scan FTIR spectrometer. The laser beam, typically of wavelength 248 or 193 nm, passed the White cell and was reflected two to six times with two external mirrors to efficiently photodissociate a flowing mixture to produce free radicals. Bandpass filters and an undersampling technique were employed to reduce the data acquisition time. IR absorption spectra of gaseous reaction intermediates such as CH3OO,1 CH3C(O)OO,2 and C6H5CO3 have been recorded using this technique; all spectra were previously unobserved. One of the advantages of this technique in determining the structures of free radicals is to distinguish absorption bands of different isomers. For example, distinct absorption spctra of various isomers of CH3SO2,4 CH3SOO,5 and CH3OSO6 have been clearly identified using this technique.

The Criegee intermediates are carbonyl oxides that play key roles in the reactions of ozone with unsaturated hydrocarbons; these reactions thus become an important mechanism for the removal of unsaturated hydrocarbons and for the production of OH in the troposphere. No direct spectral identification of even the simplest gaseous intermediate CH2OO (formaldehyde oxide) has been reported. We recorded the transient infrared absorption spectrum of CH2OO, produced from the reaction CH2I + O2 in a flow reactor, with this technique. The five observed bands near 1435, 1286, 1241, 908, and 848 cm 1 provide definitive identification of this intermediate on comparison of anharmonic vibrational wavenumbers and relative IR intensities predicted using quadratic force field obtained with the NEVPT2 method implemented in the MOLPRO quantum chemistry package using the CASSCF(8,8) reference wave function. Observed rotational contours also agree with those simulated based on rotational constants predicted with the B3LYP method. Observation of the out-of-plane CH2-wagging ( 8) mode near 848 cm 1 with a characteristic c-type contour showing a prominent Q-branch further supports the assignment of the observed features to a planar CH2OO.7 The observed vibrational wavenumbers indicate that a zwitterion rather than a diradical describes this intermediate appropriately. Partially resolved vibration-rotational spectra at resolution 0.25 cm 1 and their analysis will also be presented. The yield of CH2OO, as a function of pressure of O2 and N2, and the decay kinetics will also be discussed. 1. D.-R. Huang, L.-K. Chu, Y.-P. Lee, J. Chem. Phys. 127, 234318 (2007). 2. S.-Y. Chen, Y.-P. Lee, J. Chem. Phys. 132, 114303 (2010). 3. S.-Y. Lin, Y.-P. Lee, J. Phys. Chem. A 116, 6366 (2012). 4. L.-K. Chu, Y.-P. Lee, J. Chem. Phys. 124, 244301 (2006). 5. L.-K. Chu, Y.-P. Lee, J. Chem. Phys. 133, 184303 (2010). 6. J.-D. Chen, Y.-P. Lee, J. Chem. Phys. 134, 094304 (2011). 7. Y.-T. Su, Y.-H. Huang, H. A. Witek, Y.-P. Lee, Science 340, 174 (2013).


73

Spectroscopic properties of the c-C6H7 radical and its cation:

a high-level theoretical study

A. Bargholz, R. Oswald, P. Botschwina

Institut für Physikalische Chemie, Universität Göttingen, Tammannstraße 6, D-37077 Göttingen, Germany

The cyclohexadienyl radical (c-C6H7) may be considered as the prototype of intermediates that form during the initial step of oxidation and hydrogenation of aromatic compounds. Its electronic ground state ( 1

2 BX~ ) has been studied by explicitly correlated coupled cluster theory at the (R)CCSD(T)-F12x (x = a, b) level, partly in combination with the double-hybrid density functional method B2PLYP.1 An accurate equilibrium structure has been established and the ground-state rotational constants are calculated to be A0 = 5347.3 (5348.9) MHz, B0 = 5249.7 (5248.7) MHz, and C0 = 2692.5 (2685.2) MHz, with experimental values2 being given in parentheses. The calculated vibrational wavenumbers agree well with the recent p-H2 matrix IR data3 and several predictions have been made. A low value of 6.803 eV has been predicted for the adiabatic ionization energy of c-C6H7. It may be compared with a recent experimental value of 6.820 eV, as obtained from resonant two-colour two-photon ionization spectroscopy and extrapolated back to zero field.4 Owing to a moderately large change in the equilibrium structure upon ionization, the first band of the photoelectron spectrum is dominated by the adiabatic peak (100 %) and only the peaks corresponding to excitation of the two lowest totally symmetric vibrations ( 12 and 11) by one vibrational quantum have relative intensities of more than 15 %. The C6H6-H dissociation energy is calculated to be D0 = 85.7 kJ mol-1, with an estimated error of ca. 2 kJ mol-1. 1. A. Bargholz, R. Oswald, P. Botschwina, J. Chem. Phys. 138, 014307 (2013). 2. M. Nakajima, T. W. Schmidt, Y. Sumiyoshi, Y. Endo, Chem. Phys. Lett. 449, 57 (2007). 3. M. Bahou, Y.-J. Wu, Y.-P. Lee, J. Chem. Phys. 136, 154304 (2012). 4. O. Krechkivisk, T. W. Schmidt, personal communication.


74

Observation of orientation dependent electron transfer in inelastic

molecule-surface collisions

Nils Bartels,a) Kai Golibrzuch,a) Christof Bartels,a) Chen Li,b) Daniel J. Auerbach,b) Alec M. Wodtke,a,b) Tim Schäfer a)

a) Institut für Physikalische Chemie, Georg-August University of Göttingen, Tammannstraße 6, 37077 Göttingen, Germany.

b)Department of Dynamics at Surfaces, Max Planck Institut für biophysikalische Chemie, Am Faßberg 11, 37077 Göttingen, Germany.

Molecules must typically point in specific relative directions to participate efficiently in energy transfer and reactions. For example, Förster energy transfer favors specific relative directions of each molecule’s transition dipole1 and electron transfer between gas-phase molecules often depends on the relative orientation of orbitals2, 3. Proper orientation can allow reactants to closely approach one another allowing formation of the chemical transition state4 leading to products, a method perfected by enzymes whose active sites promote specific reactions by orienting reactants5. Despite a vast body of knowledge on orientation effects, we know little about how it affects reactivity at surfaces. Surface chemical reaction rates can be many orders of magnitude faster than their gas-phase analogs, a fact that underscores their importance for catalysis. One reason for this is the labile change of oxidation state that commonly takes place upon adsorption. By transferring electrons efficiently to or from the adsorbate, the process of bond weakening and/or cleavage is initiated, chemically activating the reactant6. Here we show that a simple chemical process, the vibrational relaxation of NO, is dramatically enhanced when the molecule approaches a Au(111) surface with the N-atom oriented towards the surface. The orientation of the molecule controls the rate of electron transfer from the surface to the molecule and thereby the rate of vibrational relaxation7-9. These measurements provide a means to directly observe the influence of orientation on electron transfer occurring in molecule-surface collisions. Moreover, the results demonstrate the importance of properly treating orientation in developing first principles theories of surface chemical reactivity, particularly when electron transfer is involved. 1. T. Förster, Ann. Phys. 2 (1948). 2. R. J. Beuhler, R. B. Bernstein, and K. H. Kramer, J. Am. Chem. Soc. 88 (1966). 3. P. R. Brooks et al., J. Am. Chem. Soc. 129 (2007). 4. D. Skouteris et al., Science 286 (1999). 5. T. C. Bruice, and F. C. Lightstone, Acc. Chem. Res. 32 (1999). 6. B. Yoon et al., Science 307 (2005). 7. R. Cooper et al., Angew. Chem. Int. Ed. 51 (2012). 8. J. W. Gadzuk, J. Chem. Phys. 79 (1983). 9. A. M. Wodtke, D. Matsiev, and D. J. Auerbach, Prog. Surf. Sci. 83 (2008).


75

Investigation of Combustion Behaviour and Flame Propagation within a

One-Cylinder Internal Combustion Engine

A. Thrun, F. Temps

Institute of Physical Chemistry, Christian-Albrechts-University Kiel, Max-Eyth-Straße 1, Kiel, Germany

To understand the underlying combustion mechanism we investigated a hydrocarbon/air-fueled one-cylinder spark ignition combustion engine for future development and optimization using OH laser-induced fluorescence (LIF). In particular, we were interested in the experimental studies of the reactive flows and the flame front inside the combustion chamber in order to determine their physical and chemical properties. Our first aim was to develop a setup for the investigation of fuel distribution and mixture, flame front propagation, pressure rise and piston speed. The 25 cm³ combustion chamber could additionally be operated with a small fan located at the top center to ensure mixing of fuel and air and to generate turbulent combustion conditions. For characterization of the flame front, both the flame chemiluminescence and laser-induced fluorescence (LIF) of OH radicals were recorded. For the LIF imaging the A2Σ+←X2Π (υ = 1→0) band at = 283 nm was excited by a laser sheet and the fluorescence was detected off-resonant around = 310 nm (A-X (υ = 1→0)). The experiments revealed a dramatic difference between the operation with and without additional fan, both in terms of flame speed and pressure rise for propane/air mixtures. In the unstirred mixture, a peak pressure of Δpmax ~ 2.0 bar was observed at tΔp,max = 15 ms after the ignition and yielded a maximum piston speed of about vmax = 85 km/h. In case of the stirred operation, the turbulent conditions increased the flame velocity, pressure rise and piston speed by a factor of 2. The OH-LIF and chemilumescence imaging indicated a highly disturbed system due to wrinkling and rupture of the flame front. The maximum efficiency of the combustion process showed a strong dependency on the delay time between the start of the fan and the ignition event. The maximum pressure rise of Δpmax = 4.0 bar was reached after a delay time of Δt = 500 ms. Further increase of Δt only led to a decrease of ignition probability, up to the point where the propane/air mixture could not be ignited anymore. In case of propene/1-butene/air mixtures, the same dependence on the fan delay was observed, but no indication of decreasing ignition probability. For further investigation and a better understanding of this behaviour, the influence of the turbulence-flame kernel interaction is investigated by the means of particle image velocimetry (PIV) and ignition delay times at the location of the spark plug.


76

Rotational Analysis of the Ã − X System of the

C3Ar van der Waals complex

Anthony J. Merer,a,b) Yen-Chu Hsu,a) and Yi-Jen Wang a)

a) Institute of Atomic and Molecular Sciences, Academia Sinica,

P. O. Box 23-166, Taipei 10764, Taiwan, R. O. C. b) Dept. of Chemistry, University of British Columbia, Vancouver, B.C., Canada V6T 1Z1

A band contour program for asymmetric top molecules has been used to assign the rotational structures of the 25024, 25029, 25431, and 25435 cm−1

bands of C3Ar. The former two bands lie just to the red of the 0 2− 0 - 0 0 0 band of the Ã1Πu − X1Σ+

g system of C3 while the latter two bands lie to the red of the 0 4− 0 - 0 0 0 band. The 25435 and 25029 cm−1 bands are type C (perpendicular) transitions. The 25029 cm−1

band is too weak for its lower state rotational constants to be determined independently; its lower state was therefore assumed to be the same as that of the 25435 cm−1

band. The rotational constants derived from these bands (in cm−1) are: T0 = 25434.882(4), A' = 0.4425(13), B' = 0.06613(37), C' = 0.05394(74), A" = 0.45507(143), B" = 0.05971(259), C" = 0.05458(251) and T0 = 25028.504(10), A' = 0.4440(15), B' = 0.06534(66), C' = 0.05402(165). Only even-K levels are present in the lower state, so that, with data for K" = 1 levels not available, the constants B" and C" are highly correlated. The A constants of these states are all about 5% larger than the B constants of the relevant levels of free C3, indicating that the complex has the shape of an italic letter T, with the top of the T tilted by about 13o

relative to its stalk. The 25431 and 25024 cm−1 bands are

type A transitions. Because of overlapping resulting from the ΔK = 0 selection rule, combined with the weakness of the bands, only limited data could be obtained.


77

Vibrational Level Calculations for the Ground Electronic States of

C3 and C3Ar

Yi-Ren Chen, Anthony J. Merer, and Yen-Chu Hsu

Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei 10764, Taiwan, R. O. C.

Potential energy surfaces for the ground electronic states of C3 and C3Ar have been calculated at the level of CCSD(T)/aVQZ and CCSD(T)/VQZ,1 respectively. 8993 points were computed to generate the C3 potential using as valence coordinates the C-C bond length (1.1-1.5 Å) and ∠C-C-C = 70-179.5°. 46550 points were computed to obtain a four-dimensional (4D) potential for C3Ar, within the ranges ∠C-C-C = 112-179.5°, R (vdW bond length from Ar to the center of mass of C3) = 3.4-6.0 Å, φ (azimuth angle between the vdW bond and the principal axis of C3) = 0-180°, and θ (colatitude angle) = 0-180°; the C-C bond length in C3 was fixed at r = 1.2980625Å. The Heidelberg Multiconfiguration time-dependent Hartree package2 was used to calculate the vibrational levels of C3 and C3Ar using Jacobi coordinates. A complication occurs in the valence-to-Jacobi coordinate transformation for C3Ar: one of the Jacobi coordinates (the vector from the third carbon atom to the center of mass of the other two carbon atoms) changes its vector length as the C3 bond angle changes, even though the C-C bond length was kept constant during the 4D potential computation. Hence we cannot simplify the Hamiltonian to four dimensions. To avoid having to perform six-dimensional ab initio calculations, it was assumed that the presence of an Ar atom does not change the C3 potential in regions outside our calculations. In other words, our calculated C3 potential could be added to our 4D C3Ar potential to extend the C3Ar potential up to six dimensions. This assumption is reasonable if we are interested only in vibrational levels lying below 800 cm−1, where the C-C stretching vibrations are not excited. The results will be compared with other work3 and experimental observations.4 1. MOLPRO, version 2010.1, a package of ab initio programs, H.-J. Werner, P. J. Knowles, G. Knizia, F. R.

Manby, M. Schütz, and others, see http://www.molpro.net. 2. G. A. Worth, M. H. Beck, A. Jäckle, H.-D. Meyer, F. Otto, M. Brill, and O. Vendrell, The MCDTH package,

version 8.4, Heidelberg University, Heidelberg, Germany, 2011. 3. M. Mladenović, S. Schmatz, and P. Botschwina, J. Chem. Phys. 101, 5891 (1994) and references therein. 4. G. Zhang, B.-G. Lin, S.-M. Wen, and Y.-C. Hsu, J. Chem. Phys. 120, 3189 (2004).


78

FTMW Spectroscopy and Determination of the

3-D Potential Energy Surface for Ar–CS

C. Niida,a) M. Nakajima,a) Y. Sumiyoshi,b) Y. Ohshima,c) H. Kohguchi,d) and Y. Endoa)

a) Department of Basic Science, The University of Tokyo, Komaba 3-8-1, Tokyo, Japan b) Department of Chemistry and Chemical Biology, Gunma University,

Maebashi, Gunma, Japan c) Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki, Japan

d) Department of Chemistry, Hiroshima University, Higashi-Hiroshima, Japan Pure rotational transitions of the Ar–CS complex have been observed by FTMW spectroscopy for the normal species with vCS = 0, 1, and 2 and for C34S in the ground vibrational state. The complex was produced in a supersonic jet by discharging 0.1% of CS2 diluted in Ar. Ordinary FTMW spectroscopy was applied for transitions below 40 GHz, and double resonance spectroscopy for those above 40 GHz. Both a-type and b-type transitions were observed with K up to 2 for the rigid asymmetric top notation. All the observed transition frequencies have been utilized to determine a 3-dimentional potential energy surface for the complex, explicitly considering the dependence of the CS stretching motion for the intermolecular interaction between Ar and CS, which is indispensable to analyze the transitions for the excited vibrational states and those of the 34S species simultaneously. High-level ab initio calculations, CCSD(T)-F12b/aug-cc-pV5Z, for almost 2000 grid points have been performed to obtain the initial 3-D potential. The calculated energy at each point has been fitted to an analytical function with 57 determinable parameters. The potential parameters have been improved by fitting the observed transition frequencies, where ro-vibrational energies were calculated by diagonalizing Hamiltonian matrices with dimensions up to 18,000 using a procedure similar to that reported previously.1 However, the procedure is much simpler for the present system, since CS is a closed shell molecule. All the 95 observed transition frequencies have successfully been fitted using 15 adjustable parameters with a standard deviation of the fit to be 0.028 MHz, almost within their experimental accuracies.

1. Y. Sumiyoshi and Y. Endo, J. Chem. Phys. 123 054325 (2005).


79

Jet-cooled excitation spectra of large benzannulated benzyl radicals:

9-anthracenylmethyl (C15H11) and 1-pyrenylmethyl (C17H11)

Gerard D. O’Connor, George B. Bacskay, Gabrielle V.G. Woodhouse, Tyler P. Troy, Klaas Nauta, Scott H. Kable and Timothy W. Schmidt

School of Chemistry, The University of Sydney, NSW 2006, Australia

The jet-cooled D1 ← D0 excitation spectra of two benzannulated benzyl radicals (BBRs), 9-anthracenylmethyl (9-AnMe) and 1-pyrenylmethyl (9-PyMe), have been obtained using mass-resolved resonant two-colour two-photon ionization spectroscopy (R2C2PI). Analysis of the spectra in view of symmetry and calculated vibrational frequencies indicate significant vibronic coupling. From the spectrum of 9-AnMe we elucidate significant anharmonicity in the excited state. This anharmonic behaviour is examined computationally through both TD-DFT and ab initio methods. Excited state properties of 9-AnMe and 1-PyMe are examined with reference to the existing spectra of smaller BBRs. Trends in the observed spectra of BBRs allow spectroscopic properties of larger BBRs to be predicted. These predictions suggest the D1 ← D0 transitions of large BBRs are unlikely to be carriers of the diffuse interstellar bands.


80

Pure beams of chromophore-water clusters: towards the investigation of

the photochemistry of aggregate systems in the molecular frame

D. A. Horke,a) Y.-P. Chang,a) S. Trippel,a) T. Mullins,a) S. Stern,a,b) J. Küpper a,b,c)

a) Center for Free-Electron Laser Science, DESY, Notkestraße 85 22607 Hamburg, Germany b) Department of Physics, University of Hamburg, Luruper Chaussee 149,

22761 Hamburg, Germany c) The Hamburg Center for Ultrafast Imaging, Luruper Chaussee 149,

22761 Hamburg, Germany We have previously demonstrated that the electrostatic deflection technique can be used for the efficient separation of different species present in supersonically expanded molecular beams, such as different conformers1 or different cluster stoichiometries.2 Here, we show how this technique can be used to create pure molecular beams of cold chromophore(H2O) clusters, well separated from isolated water and chromophore molecules, as well as higher-order clusters. This is shown in the figure below for indole(H2O) clusters. We will present details on the separation of individual quantum states or species of water, chromophore, and chromophore-water clusters. We explore in how far these state-selected and isolated species can be laser aligned and mixed-field oriented.3 These controlled samples of complex molecules are ideally suited for experiments aimed at extracting molecular-frame information from photofragment or photoelectron imaging,4 as well as x-ray or electron diffraction experiments.5

Figure 1: Transverse spatial profile of a molecular beam of indole in wet Helium carrier gas following passage through an electrostatic deflector. A pure sample of indole(H2O) is obtained at positions of ~2.5 mm from the center of the undeflected beam.2

1. F. Filsinger, et. al., Phys Rev. Lett. 100, 133003 (2008); ibid., Angew. Chem. Int. Ed. 48, 6900 (2009). 2. S. Trippel, et. al., Phys. Rev. A 86, 033202 (2012). 3. L. Holmegaard et. al., Phys. Rev. Lett. 102, 023001 (2009). 4. L. Holmegaard et. al., Nat. Phys. 6, 428 (2010). 5. F. Filsinger, et. al., Phys. Chem. Chem. Phys. 13, 2076 (2011); A. Barty et. al., Annu. Rev. Phys. Chem. 64,

415 (2013).


81

Conformer-specific reactions with Coulomb-crystallized ions

D. Rösch,a) D. Willd,a) S. Willitsch,a) Y.-P. Chang,b) K. Długołecki,b) J. Küpper b,c,d)

a) Department Chemie, Universität Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland

b) Center for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany c) Department of Physics, University of Hamburg, Luruper Chaussee 149,

22761 Hamburg, Germany d) The Hamburg Center for Ultrafast Imaging, Luruper Chaussee 149,

22761 Hamburg, Germany Different conformations (structural isomers) of prototypical complex molecules can exhibit different reactivities, due to differences in their “chemical shape” and their electronic properties. This provides perspectives to manipulate the outcome of a chemical reaction by selecting specific molecular conformations.1 To explore this dependence in bimolecular reactions, we study gas-phase reactive collisions between conformer-selected neutral molecules of 3-aminophenol1 and Coulomb crystals of laser-cooled Ca+ ions.2 3-aminophenol exhibits two conformations, cis and trans, with distinct permanent electric dipole moments. They can be spatially separated in a molecular beam passing through an electrostatic deflector that creates inhomogeneous electric fields.1 Coulomb crystals of spatially localized Ca+ ions in an ion trap provide a suitable stationary target for the present reactive scattering study, due to high sensitivities to a level of single reaction events.2 We present experimental results of conformer-specific second-order reaction rates. The analysis is supported by corresponding theoretical calculations. 1. F. Filsinger et al, Phys. Rev. Lett. 100, 133003 (2008); F. Filsinger et al, Angew. Chem. Int. Ed. 48, 6900

(2009). 2. S. Willitsch, Int. Rev. Phys. Chem. 31, 175 (2012).


82

Fast 1,2-acyl group migration in the gas phase oxidation of ketone radicals

and their unsaturated hydrocarbon analogs

A. M. Scheer, O. Welz, D. L. Osborn, C. A. Taatjes

Combustion Research Facility, Sandia National Laboratories, MS 9055, Livermore, CA 94551 USA

A thorough understanding of radical rearrangement reactions is vital for building accurate kinetic models to describe complex oxidation or autoignition systems and for designing productive organic syntheses. Here we report that a 1,2-acyl group migration1 is facile in the gas phase and is important in oxidation of ketones (R2C=O). An analogous rearrangement is important in the oxidation of methylene-containing compounds (R2C=CH2). In our experiments, laser-photolytically produced Cl atoms abstract hydrogen atoms from the ketone and the resulting radicals react with a large excess of O2. Products are monitored as a function of reaction time, mass, and photoionization energy using Multiplexed Photoionization Mass Spectrometry (MPIMS) with tunable ionizing radiation provided by the Chemical Dynamics Beamline at the Advanced Light Source.

Primary radicals formed by abstraction from the γ-position relative to the ketone carbonyl group (see figure) can undergo a rapid 1,2-acyl group migration. CBS-QB3 calculations indicate the 1,2-acyl group migration occurs with a barrier of about 9 kcal/mol and is a single step reaction as shown in the figure. This rearrangement yields a more stable radical depending on the degree of substitution at the initial β-site. Without rearrangement, radicals derived from methyl-tert-butyl ketone (MTbuK) and di-tert-butyl ketone (DTbuK) can add O2, but cannot subsequently undergo HO2-elimination to yield a closed-shell unsaturated hydrocarbon. However, the experiments show that, not only are the products of such HO2-elimination processes observed in MTbuK and DTbuK oxidation, they represent the dominant channel for these fuels at 550 K and 8 Torr. Methyl-isopropyl ketone (MIPK) has both a tertiary atom at the β site and primary H atoms at the γ position of the isopropyl group. After O2-addition, radicals originating from either site can undergo HO2-elimination without rearrangement, forming 3-methyl-3-buten-2-one. However, 1,2-acyl group migration from the initial primary radical results in a secondary radical that yields 3-penten-2-one upon HO2-elimination. A 2:1 branching ratio is found for the yield of 3-penten-2-one : 3-methyl-3-buten-2-one, which is invariant to changing O2 concentration by a factor of four. This indicates that the rearrangement of the primary radical (γ-position) is rapid relative to O2-addition at [O2] = 3 1016 cm-3 and implies that the tertiary radical (β-position) is the exclusive source of the 3-methyl-3-buten-2-one product, despite the fact that the barrier to this elimination is calculated to lie above the R + O2 entrance channel. Finally, such 1,2-rearrangement is also facile for intramolecular radical attack on C=C bonds; an analogous rearrangement is observed in 2,3,3-trimethyl-1-butene oxidation. Acknowlegment: This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under contract DE-AC04-94AL85000. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the United States Department of Energy under contract DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory.

1. C. L. Karl, E. J. Maas, W. Reusch, J. Org. Chem. 37, 2834 (1972).

RC

CR1,2

OCH2

RC

CR1,2

OCH2

RC

O

CH2CR1,2


83

Laser Induced Inhibition of Cluster Growth (LIICG) -

A new method to measure electronic spectra

S. Chakrabarty,a) M. Holz,a) A. Banerjee,a) D. Gerlich,b) and J.P. Maier a)

a) Departement of Chemistry, University Basel, Klingelbergstr. 80, CH-4056 Basel, Switzerland

b) Departement of Physics, TU Chemnitz, Reichenhainer Str. 70, D-09126 Chemnitz, Germany

A novel technique to measure spectra of molecular cold ions at temperatures below 10 K has been developed and tested on an electronic transition of N2

+. The apparatus involved utilizes a combination of two quadrupole mass spectrometers coupled with a cryogenically cooled temperature variable 22-pole trap. Inside the trap confined ions undergo collisions with helium relaxing all of its degrees of freedom. At sufficiently high number densities of buffer gas, ternary reactions resulted in the formation of weakly bond van der Waals clusters by the attachment of one helium atom to the ion. A rotationally resolved A2

u(v′ = 2; J′) X 2g

+ (v" = 0; J") electronic spectrum of N2

+, held at 5 K inside the trap, was measured by monitoring the attenuation in the rate of growth of N2

+ · · · He upon laser excitation. The translational temperature of the ion ensemble was determined from the Doppler profile of the R11 line originating from J" = 0.5 in the v" = 0 level of the electronic ground state of ortho-N2

+ to T = (49 6) K. One of the major motivations behind the development of LIICG is to measure electronic spectra of carbonaceos ions at low temperatures related to the identification of carriers of Diffuse Interstellar Bands. It is essential to study the possible candidates under conditions similar to the interstellar medium for proper comparison.


84

Seasonal Measurements of Atmospheric OH Radicals

on the West Coast of Ireland

M. Adam,a) J. McGrath,a) F. Rohrer,d) R.L. Mauldin III,b,c) B. Bohn,d) C. Monahan,a) C.O’Dowd,a) and H. Berresheim a)

a) School of Physics and Center for Climate and Air Pollution Studies, National University of Ireland Galway, Ireland

b) University of Helsinki, Finland; c) University of Colorado, USA d) Institute for Energy and Climate Research (IEK-8), Research Center Jülich, Germany

Measurements of the OH radical, sulfuric acid and methane sulfonic acid with the Chemical Ionisation Mass Spectrometer (CIMS) have been carried out in the marine atmosphere of Mace Head, Ireland since May 2010. Monthly mean average OH values range from 2.1 105 cm-3 in winter to 2.3x106 cm-3 in summer in background marine air. SO2 and NO mixing ratios were mostly between 100-200 pptv and less than 100 pptv, respectively. The concentration of OH is obtained from the difference of a signal measurement during which isotopically labelled 34SO2 is added to the sample flow in order to obtain 34H2SO4 and a background measurement when propane is added to the signal measurement which scavenges >99% of the OH present. However, background levels have been exceeding expected values which points to the presence of an unknown oxidant, here called X, possibly playing an important role in the oxidation capacity of the marine atmosphere. OH correlated highly with J(O1D) with R = 0.75. In some cases measured H2SO4 concentrations were up to a factor of 3.5 higher compared to results from just considering the main production pathway OH + SO2 and H2SO4 deposition to aerosol particles. In such cases the H2SO4 balance could only be closed by including the unknown SO2 oxidant X which showed a similar diurnal pattern as the OH radical indicating photochemical source(s). Possible candidates which may thus rival OH reactions might be either Criegee biradicals or perhaps halogen radicals. However, corresponding kinetic data are currently lacking. A calculation of the turnover rate of gaseous H2SO4 to new particle formation has been carried out to elucidate the possible contribution of H2SO4 to aerosol surfaces and this is found to contribute on a number of days to new particle formation events.


85

Imaging Inelastic Scattering of Methyl Radicals with Gases and Reactive

Scattering of Chlorine Atoms with Propene

Thomas J. Preston,a) Ondrej Tkáč,a) Greg T. Dunning,a) Alan G. Sage,a) Stuart J. Greaves,b) and Andrew J. Orr-Ewing a)

a) School of Chemistry, University of Bristol, Cantock’s Close, Bristol, United Kingdom b) Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, United Kingdom

Current velocity-map imaging experiments at Bristol follow gas-phase collision dynamics in two chemical systems. In the first experiment, photolysis of CD3I entrained in a molecular beam generates CD3 radicals and the supersonic expansion removes most of their excess internal energy. These rotationally cold polyatomic radicals scatter from He, Ar, H2, or D2 in a second molecular beam. The collision can transfer the translation energy to rotational energy in CD3, and velocity-map ion imaging with state-selective ionization records both the quantum state and velocity of the scattered CD3 fragments. Scattered methyl radicals with low

J scatter predominantly in the forward direction, but as the collision transfers more energy to the internal modes of CD3, the radical becomes more side-scattered. Increasing angular scattering with J is consistent with the application of more torque at smaller impact parameters, and these results are in quantitative agreement with recent quantum close-coupling calculations by Paul Dagdigian and Millard Alexander. A separate machine uses velocity-map ion imaging to monitor the HCl born from the reaction between propene and photolytically generated Cl. The reaction is exothermic by about 60 kJ/mol, which is enough energy to excite HCl to v = 1. Imaging HCl in v = 1 shows forward scattering, with the reaction populating only the lowest few rotational levels. The speed distributions of the HCl products extend to the limit dictated by the thermochemistry of the reaction, suggesting that a stripping-type mechanism may dominate the dynamics.


86

Probing the low-temperature chain-branching mechanism for n-butane

autoignition chemistry: Pressure-dependent measurements of ketohydroperoxide formation in pulsed-photolytic n-butane oxidation

A. J. Eskola, O. Welz, I. O. Antonov, L. Sheps, J. D. Savee, D. L. Osborn, C. A. Taatjes

Combustion Research Facility, Sandia National Laboratories, 7011 East Avenue,

MS 9055, Livermore, California 94551, USA Product formation in low-temperature (575 K – 650 K) pulsed-laser photolytic Cl-initiated oxidation of n-butane was investigated using multiplexed photoionization time-of-flight mass spectrometry (MPIMS) employing the Advance Light Source synchrotron radiation for ionization. Both low (4 – 40 Torr) and high (740 – 790 Torr) pressure flow reactors were coupled to MPIMS in order to investigate the effect of pressure on product yields and kinetics. These experiments probe the time-resolved and isomer-specific formation of products following the laser-photolytic initiation of the oxidation. They are sensitive to the first steps of butane oxidation: the reaction of butyl radicals with O2 and subsequent reactions of butyl peroxy (ROO) radicals and their hydroperoxybutyl (QOOH) isomers.

At low pressure, the main oxidation products were observed at m/z = 56 (C4H8), associated with chain-terminating HO2 loss from ROO, and m/z = 72 (C4H8O) from chain-propagating OH formation. Under low-pressure conditions time-resolved formation of ketohydroperoxides (m/z = 104) was also observed, originating from the “second” oxygen addition to QOOH radicals and subsequent internal abstraction/dissociation leading to ketohydroperoxide + OH. Further decomposition of ketohydroperoxide to oxy-radical (QO) + OH, releasing the second OH, is a radical chain-branching channel, which promotes or even accelerates oxidation. At low pressure, the time-behavior of m/z = 104 signal was substantially slower than the formation of products at m/z = 56 and 72.

At high pressure, the yield of oxidation products at m/z = 56 (C4H8) and 72 (C4H8O) was clearly suppressed with respect to low pressure conditions, whereas signal intensity associated with ketohydroperoxide formation became stronger. In addition, formation of m/z = 104 signal at high pressure was significantly faster than under low-pressure conditions, showing closely similar time-behavior with the m/z = 56 signal, which is the main oxidation product at high pressure. Increasing contribution from the signal at m/z = 104 at higher pressure likely originates from the combined effects of increasing hydroperoxybutyl radical interception at higher O2 concentrations and faster internal abstraction/dissociation of hydroperoxy-butylperoxy (OOQOOH) radical to ketohydroperoxide at higher total pressure.

Acknowledgment: This work was supported as part of the Saudi Aramco “Kinetics Cluster of Excellence” under a cooperative research and development agreement (CRADA) between Sandia National Laboratories and Aramco Services Company, a U.S.-based subsidiary of Saudi Aramco, the state-owned national oil company of Saudi Arabia (CRADA SC10/01773.00, ASC Contract No. 6500007287). Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under contract DE-AC04-94-AL85000. The participation of L.S., O.W., I.O.A, J.D.S., and D.L.O. and the development of the experimental apparatus were supported by the Division of Chemical Sciences, Geosciences, and Biosciences, the Office of Basic Energy Sciences, the U.S. Department of Energy, in part under the Argonne-Sandia Consortium on High-Pressure Combustion Chemistry (Sandia FWP # 014544). The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. DOE, also under contract DE-AC02-05CH11231 between Lawrence Berkeley National Laboratory and the U.S. DOE.


87

Spectroscopy and chemical kinetics of formaldehyde oxide (CH2OO) using

time-resolved broadband cavity-enhanced absorption spectroscopy

Leonid Sheps

Combustion Research Facility, Sandia National Laboratories, 7011 East Avenue, MS 9055, Livermore, California 94551, USA

We recently developed a novel optical probing method: time-resolved broadband cavity-enhanced absorption spectroscopy (TR-BB-CEAS). The new technique is geared towards experimental detection of transient gas-phase chemical species that may be difficult to directly observe by other means. At the heart of TR-BB-CEAS is a low-finesse optical resonator cavity, coupled to an incoherent white-light probe radiation source (Xe arc lamp). The cavity operates over a very broad spectral range, 300 – 700 nm, providing an average factor of 100 sensitivity enhancement over single-pass absorption spectrometry and making it a viable probe technique for low-density gaseous samples. The resonator is integrated into a slow-flow chemical reactor, where laser flash photolysis initiates gas-phase reactions by creating transient populations of radical species. Broadband absorption spectra, recorded with microsecond time resolution, enable deconvolution of overlapping spectral features and facilitate kinetic studies and spectroscopic assignments. The newly constructed TR-BB-CEAS apparatus was used for spectroscopic and chemical kinetic studies of formaldehyde oxide (CH2OO) – a member of an important class of Criegee intermediates, which are produced in the Earths troposphere. In 2012 Welz et al. demonstrated a way of producing large quantities of these transient species in the laboratory.1 Since then, Criegee intermediates have been the subject of intense experimental interest; several publications appeared within the last year, including one report of the UV absorption of formaldehyde oxide by action spectroscopy.2 I will present a direct absorption spectrum of the B1A′ ← X1A′ transition of CH2OO in the 300 – 450 nm wavelength region. The spectrum appears to be broader than the published action spectrum and exhibits some vibrational structure on the low-energy side. Chemical kinetic experiments using this absorption spectrum help identify the transient species as CH2OO. Formaldehyde oxide is produced by photolysis of CH2I2 in an excess of oxygen, and its formation timescale agrees very well with the published bimolecular reaction rate coefficient3 for CH2I + O2 (k298 = 1.4·10-12 cm3·s-1). Addition of a Criegee scavenger, SO2, quenches the transient absorption, and its decay rates agree with the literature value1 for the reaction CH2OO + SO2 (k298 = 4·10-11 cm3·s-1). Acknowledgment: This work was supported by Sandia National Laboratories under the Laboratory-Directed Research and Development (LDRD) program. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under contract DE-AC04-94-AL85000. 1. O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Percival, D. E. Shallcross, and C. A. Taatjes, Science

335, 204 (2012). 2. J. M. Beames, F. Liu, L. Lu, and M. I. Lester, J. Am. Chem. Soc. 134, 20045 (2012). 3. A. J. Eskola, D. Wojcik-Pastuszka, E. Ratajczak, and R. S. Timonen, Phys. Chem. Chem. Phys., 8, 1416

(2006).


88

Phototautomerization of CH3CHO to CH2=CHOH at

Atmospheric Pressure of N2.

Miranda Shaw,a) Alexander Clubb,a) Balint Sztaray,b) David L. Osborn,c) Meredith J. T. Jordan,a) Scott H. Kable a)

a) School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia b ) Dept of Chemistry, University of the Pacific, Stockton, CA 95211, USA

c) Combustion Research Facility, Sandia Nat’l Laboratories, Livermore, CA 94511, USA We have measured the quantum yield for photolysis and photo-tautomerization of acetaldehyde at a variety of wavelengths ( = 300 – 330 nm) and pressures (pacet = 2-20 Torr and pN2 = 0-760 Torr). Photolysis was carried out in a static cell, placed inside an evacuated FTIR spectrometer, using a pulsed, frequency-doubled dye laser. The sample was irradiated at 10 Hz, for 7 minutes, whilst recording the FTIR spectrum every 30 seconds. Stable reaction products were identified by FTIR spectroscopy, revealing the production of primary photolysis products: CO and CH4, and secondary products of photolysis to HCO + CH3: CO2, C2H6, H2CO, (CH3)2CO, and (CH3CO)2. The primary photo-tautomerization product: vinyl alcohol, VA (CH2=CHOH) was observed at all wavelengths and pressures. In addition, the production of 1-propanol (CH3CH2CH2OH) was observed, which was attributed to the secondary reaction of VA with primary CH3 radicals, followed by H addition. The photolysis quantum yield, ph was determined to be between 5 and 80% depending on pressure and wavelength. ph was reduced with longer wavelength and with increased pressure of N2. Our values of ph are in broad agreement with previously published values by Horowitz and Calvert1 and Moortgat and co-workers.2 Previously, we reported the photo-tautomerization quantum yield, VA, for neat CH3CHO.3 Here we report VA under atmospherically realistic conditions of 1 atm of N2. At 1 atm, the quantum yield for VA production increased from ~1% at 300 nm to a peak of 5% at 320 nm, reducing to 1% again at 330 nm. When the production of 1-propanol is included, the overall photo-tautomerization quantum yield was as high as 17% at 320 nm and 1 atm N2.. In general, VA increased as N2 pressure was lowered, with a maximum of VA = 23% for irradiation of 10 Torr of neat CH3CHO at 320 nm. The production of enols under atmospheric conditions might have a significant effect on the yield of organic acids in the troposphere, the production of which is generally under-estimated in atmospheric models. For example, VA will react facilely with OH radicals and in a couple of subsequent reaction steps produce formic acid. If photo-tautomerization is a general feature of aldehyde and ketone photochemistry then this mechanism may provide the origin of the missing organic acid yield in atmospheric models. 1. A. Horowitz, J.G. Calvert, J. Phys. Chem. 86, 3105 (1982). 2. G.K. Moortgat, H. Meyrahn, P. Warneck, Chem. Phys. Chem., 11, 3896 (2010). 3. A.E. Clubb, M.J.T. Jordan, S.H. Kable, D.L. Osborn, J. Phys. Chem. Lett., 3, 3522 (2012).


89

Electronic and Infrared Spectroscopy of Unsaturated Hydrocarbons of

Astrophysical Interest

D. Zhao,a) A. Walsh,a) K. Doney,a) M.A. Haddad,b) W. Ubachs,b) H. Linnartz a)

a) Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands;

b) LaserLaB, Department of Physics and Astronomy, VU University, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands

To date, about 180 different molecules have been identified in the interstellar medium (ISM) and circumstellar shells. Many of them are unsaturated hydrocarbons, such as carbon-chain radicals. In this presentation, we discuss electronic and infrared spectroscopic laboratory studies on astrophysically relevant hydrocarbon species. In our experiments, the supersonically expanding plasma, generated in a high-pressure gas discharge or by electron impact ionization, is used to produce ions, exotic radicals and complex molecules, and to provide a laboratory environment to simulate the cold, harsh conditions in ISM. Electronic spectra are studied by a highly sensitive cavity ring-down (CRDS) spectrometer,1,2 and an optomechanical shutter modulated BroadBand Cavity Enhanced Absorption Spectroscopy (BBCEAS) instrument.3,4 The former is used to measure narrow molecular features in the laboratory to provide accurate molecular data for simple interstellar molecules like C3 and l-C6H.1,2 The latter is a recently developed, unique and fully operational laboratory instrument for fast recording of optical survey of plasmas, aiming to test the absorption features observed in diffuse translucent clouds, known as the diffuse interstellar bands (DIBs).3,5

High-resolution mid-infrared spectroscopy is studied in a third experiment using our Supersonic Plasma InfraRed Absorption Spectrometer (SPIRAS), which employs a sing-frequency single-mode cw OPO as an infrared light source, and cw-CRDS as detection tool. A hardware-based multi-trigger and timing scheme is developed to apply continuous-wave CRDS to pulsed plasma.6 The resulting accurate molecular data can be used to interpret the ro-vibrational transitions in the THz/submillimeter region, supporting observational surveys at ALMA. 1. D. Zhao, M.A. Haddad, H. Linnartz H, W. Ubachs, J. Chem. Phys. 135,044307 (2011). 2. M. Schmidt, J. Krelowski, G. Galazudinov, D. Zhao, M.A. Haddad, W. Ubachs, H. Linnartz, MNRAS,

submitted (2013). 3. A. Walsh, D. Zhao, W. Ubachs, H. Linnartz, J. Phys. Chem. A, in press, DOI: 10.1021/jp310392n, (2013). 4. A. Walsh, D. Zhao, H. Linnartz, Rev. Sci. Instrum. 84, 026108 (2013). 5. IAU Symposium 297: the Diffuse Interstellar Bands, May 20-24, 2013, Noorwijkhout, the Netherlands.

(http://iau297.nl). 6. D. Zhao, J. Guss, A. Walsh, H. Linnartz, Chem. Phys. Lett.. 565,132(2013).


90

Reactivity of Criegee Intermediates CH2OO and CH3CHOO:

Direct Detection and Conformer-Dependent Kinetics

Oliver Welz,a) Arkke J. Eskola,a) John D. Savee,a) Adam M. Scheer,a) Brandon Rotavera,a) David L. Osborn,a) Edmond P. F. Lee,b,c) John M. Dyke,b) Daniel M. K. Mok,c) Carl J.

Percival,d) Dudley E. Shallcross,e) Craig A. Taatjes a)

a) Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94550, USA b) School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK c) Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic

University, Hung Hom, Hong Kong d) School of Earth, Atmospheric and Environmental Sciences, The University of Manchester,

Williamson Building, Oxford Road, Manchester M13 9PL, UK e) School of Chemistry, University of Bristol, Bristol BS8 1TS, UK

Criegee intermediates (C.I.s), carbonyl oxides, have long been implicated as key species in the troposphere. They are formed during the ozonolysis of alkenes, which is a major tropospheric degradation process of these hydrocarbon species. Reactions of C.I.s are thought to contribute to the formation of secondary organic aerosols, OH radicals, and sulfuric acid. Until recently1,2 no gas-phase C.I. had ever been directly observed, nor had the reaction of any C.I. ever been studied in isolation, and indirect determinations of their reactions with key atmospheric species gave rate coefficients spanning orders of magnitude. Here we present the direct detection and measurements of reactions kinetics of the two simplest C.I.s, formaldehyde oxide (CH2OO) and acetaldehyde oxide (CH3CHOO),2,3 in the gas phase at 300 K and 4 Torr. We generated these C.I.s with low internal energies via the reaction of laser-photolytically produced α-iodoalkyl radicals with O2. Time-resolved multiplexed synchrotron photoionization mass spectrometry (MPIMS) allowed the unambiguous identification of CH2OO and CH3CHOO based on their masses, ionization energies, and photoionization spectra. Furthermore, the two distinct conformers of CH3CHOO, syn- and anti-, could be probed independently.3

Both CH2OO and CH3CHOO react far more rapidly with SO2 and with NO2 than models have generally assumed, suggesting a prominent role of C.I.s in tropospheric sulfate chemistry. We show that CH3CHOO displays conformer-dependent reactivity,3 with anti-CH3CHOO substantially more reactive towards H2O and SO2 than is the syn- conformer. These results shed light on the fundamental physical chemistry of Criegee intermediates and help to understand their role in the troposphere. …see also hot topic talk H-10 1. C. A. Taatjes, G. Meloni, T. M. Selby, A. J. Trevitt, D. L. Osborn, C. J. Percival, D. E. Shallcross, J. Am.

Chem. Soc. 130, 11883 (2008). 2. O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Percival, D. E. Shallcross, C. A. Taatjes, Science 335,

204 (2012). 3. C. A. Taatjes, O. Welz, A. J. Eskola, J. D. Savee, A. M. Scheer, D. E. Shallcross, B. Rotavera, E. P. F. Lee, J.

M. Dyke, D. K. W. Mok, D. L. Osborn, C. J. Percival, Science 340, 177 (2013).


91

FTIR Study of NO3 – Analysis of the 3+ 4 Band and Spin-Orbit

Constants in the Ground 2A2’ State

K. Kawaguchi,a) R. Fujimori,b) J. Tang,a) T. Ishiwata c)

a) Faculty of Science, Okayama University, 3-1-1 Tsushimanaka, Okayama 700-8530, Japan b) Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa,

Nagoya 464-8601, Japan c) Graduate School of Information Sciences, Hiroshima City University, 3-4-1 Otsuka-

Higashi, Hiroshima 731-3194, Japan

The 3+ 4 band of NO3 shows the strongest infrared absorption in the 1492 and 1472 cm-1 regions for 14N and 15N species, respectively, because the 3 fundamental band (~1060 cm-1) is predicted to have very weak intensity1 due to cancellation of an infrared transition moment and a borrowed electronic transition moment through vibronic interaction with the 2E’ state. In the present study, we report on high-resolution FTIR measurement and analysis of the 15NO3 3+ 4 band. Compared with the case of 14N species, large effect of perturbation was recognized in many K levels of 15NO3. By using previous data, it was found that the 2+ 4 level is located at a little higher energy than 3+ 4. Although a direct Coriolis interaction ( v2=1, v3(or v4)=1) is not present between these two vibrational levels, anharmonic terms k344 and k444 mix 3+ 4 and 4, 3+ 4, and 2+ 4 mixes with 2+ 4. Thus anharmonic term induced Coriolis coupling was found to be important for understanding the perturbation. The similar method was successful for the analysis of the 2 band2. It was found that the 2+2 4 level has 7.26 cm-1 higher energy than 3+ 4, and interaction parameters were determined. In the case of 14NO3, we reported the analysis of the 3+ 4 band in 20113 without considering perturbation, and many higher-order constants were needed for the fitting. When the present perturbation analysis was applied to the 14N species, those higher-order constants were not necessary for the fit, and more spectral lines could be included in the fit. The ground electronic state of NO3 is non-degenerate 2A2’. However, the existence of spin-orbit interaction in E’ vibrational states is reported. In the present study, we assumed the vibronic interaction between E’ and A2’ as h3(qe

+Q3- + qe

-Q3+) + h4(qe

+Q4- + qe

-Q4+) and estimated

effective spin-orvbit interaction constant aeff to compare the observed values. Recently, we analyzed hot band spectrum including 2A’ species of the 3+2 4 level (1927 cm-1) and noticed the existence of spin orbit interaction constant in spite of the 2A’ state, in agreement with our prediction. 1. J. F. Stanton, Mol. Phys. 107, 1059 (2009). 2. R. Fujimori, N. Shimizu, J. Tang, T. Ishiwata, and K. Kawaguchi, J. Mol. Spectrosc. 283, 10(2013). 3. K. Kawaguchi, N. Shimizu, R. Fujimori, J. Tang, T. Ishiwata, and I. Tanaka, J. Mol. Spectrosc. 268,

85(2011).

92

-- Notes --

93

Poster Session B On Display: Wednesday & Thursday

Attended Time: Wednesday 19.30 – 22.30

Poster Session B Overview

94

B-01 Hydrocarbon Radicals in Superfluid Helium Nanodroplets: Rovibrational Spectroscopy and Ab Initio Calculations

Christopher P. Moradi, Paul L. Raston, Tao Liang, and Gary E. Douberly

B-02 Assessing RAFT equilibrium constants through the use of high-level local

correlation methods João C. A. Oliveira, Ricardo A. Mata B-03 Photoionization of the methylene amidogen radical H2CN and its isomers F. Holzmeier, M. Lang, P. Hemberger, I. Fischer B-04 Infrared Spectroscopy of V+(H2O)n: Temperature Effects on Isomer

Distributions K. Ohashi, J. Sasaki, K. Judai, N. Nishi, H. Sekiya B-05 Intriguing Chemistry of Nitrogen Dioxide Dimers (N2O4) in cryogenic

Matrices H. Beckers, X.-Q. Zeng, H. Willner, G. A. Argüello B-06 Ion-pair formation in the multiphoton photodissociation of HCl studied

by observation of H+ and Cl- ions by 3D-imaging M. Poretskiy, A. I. Chichinin, C. Maul, K.-H. Gericke B-07 Laser magnetic resonance study and ab initio calculations for the O(1D)

+ VF5 reaction: deactivation and branching ratios A. A. Rakhymzhan, A. I. Chichinin, V. G. Kiselev, N. P. Gritsan B-08 Decomposition of ortho-, meta-, and para-xylyl radicals in a pyrolysis

reactor: Observation of para-xylylene as product of meta-xylyl dissociation

P. Hemberger, A. Trevitt, G. da Silva B-09 Unimolecular Reaction Dynamics of an Imidazolin-2-ylidene: Unraveling

the Complex Dissociation Mechanism of an Arduengo-type Carbene P. Hemberger, A. Bodi, T. Gerber, M. Würtemberger, U. Radius B-10 Valence Photoionization Spectra and Absolute Cross-Sections of the

Vinyl, Formyl, and Propargyl Radicals J. D. Savee, O. Welz, C. A. Taatjes, and D. L. Osborn B-11 Experimental Methods for Circular Dichroism Laser Mass Spectrometry D. Jelisavac, K. Titze, C. Logé, U. Boesl B-12 Sub-Doppler Electronic Spectra of Benzene Clusters with Atoms and

Small Molecules M. Hayashi, Y. Ohshima B-13 Photodissociation Dynamics of the Thiophenoxy Radical at 248 and 193

nm Aaron W. Harrison, Jeong Sik Lim, Mikhail Ryazanov, Greg Wang, Daniel M. Neumark

Overview Poster Session B

95

B-14 Radical chemistry involving ammonia in an astrochemical context: A step toward prebiotic chemistry ?

E. L. Zins, L. Krim B-15 Absolute rate coefficient of the gas-phase reaction between hydroxyl

radical (OH) and Hydroxyacetone (HYAC) Duy N. Vu, Victor Khamaganov, Shaun Carl, Jozef Peeters B-16 Fourier Transform Microwave/Millimeter-wave Spectroscopy of Metal-

Containing Dicarbide Radicals D. T. Halfen, J. Min, L. M. Ziurys B-17 Pure Rotational Spectroscopy of Chromium-Containing Radicals J. Min, L. M. Ziurys B-18 Photodynamics of Triphenylverdazyl radicals in solution Christoph Weinert, Boris Wezisla, Jörg Lindner, and Peter Vöhringer B-19 Investigation of Free Radicals from the Oxidation of a-Pinene by

Electron Spin Resonance M.V.Ghosh, I. Kuprov, P. Ionita

B-20 Rotationally-resolved high-resolution Laser spectroscopy and the

Zeeman effect of the 662 nm band of NO3 B-X transition S. Kasahara, K. Tada, W. Kashihara, M. Baba, T. Ishiwata, E. Hirota B-21 Ultrafast pump-probe photoelectron imaging with DUV and VUV pulses T. Horio, R. Spesyvtsev, T. Kobayashi, and T. Suzuki B-22 Glyoxal Photolysis as a Quantitative Source of HNO Studied by

Frequency Modulation Spectroscopy N. Faßheber, G. Friedrichs

B-23 The highly anharmonic systems FHF- and ClHCl-: theory and experiment P. Sebald, A. Bargholz, R. Oswald, C. Stein, P. Botschwina, K. Kawaguchi B-24 Circular Dichroism Laser Mass Spectrometry: Report of Recent Progress

and Outlook to Future Projects K. Titze, C. Logé, U. Boesl B-25 High Resolution Laser Spectroscopy of Hafnium Monofluoride A. G. Adam, L. M. Esson, A. M. Smith, C. Linton, D. W. Tokaryk B-26 Experimental and calculated hyperfine structure in the electronic

spectrum of gaseous TaS Thomas D. Varberg, Andrew J. Bendelsmith, Keith T. Kuwata

Poster Session B Overview

96

B-27 Towards Spin-Orbit Coupled Diabatic Potential Energy Surfaces for Methyl Iodide Using Effective Relativistic Coupling by Asymptotic Representation

Nils Wittenbrink, Hameth Ndome, Wolfgang Eisfeld B-28 Possible Observation of the 3A’ - 1A’ Electronic Transition of the

Methylene Peroxy Criegee Intermediate Free Radical Neal D. Kline, Terry A. Miller B-29 New Features in the 3D-Applet of the Forthcoming MOGADOC Update J. Vogt, E. Popov, R. Rudert and N. Vogt B-30 PPMODR of Metal Containing Molecules T. C. Steimle B-31 Laser Induced Fluorescence Spectroscopy of Jet Cooled NO3 Free

Radicals Masaru Fukushima, Takashi Ishiwata B-32 Hybrid QM/QM Open-Shell Local Correlation Methods for the Study of

Metal Sites in Biomolecular Catalysis M. Andrejić, R. A. Mata B-33 Geminate recombination dynamics of solvated electrons in liquid-to-supercritical methanol A. Gehrmann, J. Lindner and P. Vöhringer B-34 Experimental setup for stereoselective and enantioselective

identification and characterisation of size selected chiral metal cluster catalysts

K. Lange, B. Visser, D. Neuwirth, J. Eckhardt, M. Tschurl, U. Boesl, U. Heiz B-35 Use of Antioxidants in Animal Nutrition A. Díaz-Cruz, C. Nava Cuellar, A. Martínez García, S. Zárate Epstein, J.J. Flores Malpica,

R. Guinzberg Perrusquía B-36 Free radical products as a biomarker of early Alzheimer´s disease J. Illner, J. Laczo, M. Vyhnalek, J. Hort, A. Skoumalova B-37 Tea polyphenols act as a central coordinator of oxidative stress,

antioxidants and apoptosis-related mechanism in bleomycin-induced breast cancer cells

Ali A. Alshatwi and Vaiyapuri S. Periasamy B-38 Infrared Detection of Criegee Intermediates formed during the Ozonolysis of β-Pinene and their Reactivity towards Sulfur Dioxide J. Ahrens, P. T. M. Carlsson, M. Pfeifle, M. Olzmann, T. Zeuch

Overview Poster Session B

97

B-39 An Oleic Acid Monolayer Oxidation Study Using Quantitative Time-Resolved Vibrational Sum Frequency Generation Spectroscopy

Joscha Kleber, Kristian Laß, Gernot Friedrichs B-40 Ultrafast electronic deactivation dynamics of hydrogen-bonded self-

assemblies of the 6-oxopurines inosine and guanosine K. Röttger, F. Temps B-41 Ultrafast non-radiative dynamics of electronically excited penta-

fluorobenzene by femtosecond time-resolved mass spectrometry O. Hüter, H. Neumann, D. Egorova, F. Temps B-42 A New Continuous-Wave Infrared Stimulated Emission Experiment

beyond the Doppler Limit M. Siltanen, M. Metsälä, M. Vainio, L. Halonen B-43 Characterization of high pressure supersonic plasma source: hollow

cathode effect in direct current high pressure slit jet micro-discharge O. Votava, P. Pracna, M. Mašát, V. Svoboda, and M. Fárník

B-01 Poster Session B

98

Hydrocarbon Radicals in Superfluid Helium Nanodroplets:

Rovibrational Spectroscopy and Ab Initio Calculations

Christopher P. Moradi, Paul L. Raston, Tao Liang, and Gary E. Douberly

Department of Chemistry, University of Georgia, Athens, Georgia 30602-2556, USA

Several small hydrocarbon radicals (methyl, vinyl, and ethyl) have been generated by pyrolysis and isolated in superfluid 4He nanodroplets. The rovibrational spectrum of the v3(e ) band of the methyl radical (CH3) exhibits all five allowed transitions, and these produce population in the NK = 00, 11, 10, 22 and 20 rotational levels. The observed transitions exhibit variable Lorentzian line shapes, consistent with state specific homogeneous broadening effects. Population relaxation of the 00 and 11 levels is only allowed through vibrationally inelastic decay channels, and the PP1(1) and RR0(0) transitions accessing these levels have 4.12(1) and 4.66(1) GHz full-width at half-maximum linewidths, respectively. The linewidths of the PR1(1) and RR1(1) transitions are comparatively broader (8.6(1) and 57.0(6) GHz, respectively), consistent with rotational relaxation of the 20 and 22 levels within the vibrationally excited manifold. The nuclear spin symmetry allowed rotational relaxation channel for the excited 10 level has an energy difference similar to those associated with the 20 and 22 levels. However, the PQ1(1) transition that accesses the 10 level is 2.3 and 15.1 times narrower than the PR1(1) and RR1(1) lines, respectively. The relative linewidths of these transitions are rationalized in terms of the anisotropy in the He-CH3 potential energy surface, which couples the molecule rotation to the collective modes of the droplet. The vinyl radical has been probed with infrared laser spectroscopy in the CH stretch region between 2850 and 3200 cm-1. The assigned band origins for the CH2 symmetric (v3), CH2 antisymmetric (v2), and lone -CH stretch (v1) vibrations are in good agreement with previously reported full-dimensional vibrational configuration interaction calculations.1 For all three bands, a-type and b-type transitions are observed from the lowest symmetry allowed roconvibrational state of each nuclear spin isomer, which allows for a determination of the tunneling splittings in both the ground and excited vibrational levels. Comparisons to gas phase millimeter-wave rotation-tunneling2 and high-resolution jet-cooled infrared spectra3 reveal that the effect of the He solvent is to reduce the ground and v3 excited state tunneling splittings by 20%. This solvent-induced modification of the tunneling dynamics can be reasonably accounted for by assuming either an 2.5% increase in the effective barrier height along the tunneling coordinate or an 5% increase in the effective reduced mass of the tunneling particles. The band origins of the five CH stretch fundamentals for the He-solvated ethyl radical are shifted by < 2 cm-1 from those reported for the gas phase species.4,5 The symmetric CH2 stretching band (v1) is rotationally resolved, revealing nuclear spin statistical weights predicted by G12 permutation-inversion group theory. A permanent electric dipole moment of 0.28 (2) D is obtained via the Stark spectrum of the v1 band. The four other CH stretch fundamental bands are significantly broadened in He droplets and lack rotational fine structure. This broadening is attributed to symmetry dependent vibration-to-vibration relaxation facilitated by the He droplet environment. In addition to the five fundamentals, three a1' overtone/combination bands are observed, and each of these have resolved rotational substructure. These are assigned to the 2v12, v4+v6, and 2v6 bands through comparisons to anharmonic frequency computations at the CCSD(T)/cc-pVTZ level of theory. 1. A. R. Sharma, B. J. Braams, S. Carter, B. C. Shepler, J. M. Bowman, J. Chem. Phys. 130, 174301 (2009). 2. K. Tanaka, M. Toshimitsu, K. Harada, T. Tanaka, J. Chem. Phys. 120, 3604 (2004). 3. F. Dong, M. Roberts, D. J. Nesbitt, J. Chem. Phys. 128, 044305 (2008). 4. S. Davis, D. Uy, D. J. Nesbitt, J. Chem. Phys. 112, 1823-1834 (2000). 5. T. Häber, A. C. Blair, D. J. Nesbitt, M. D. Schuder, J. Chem. Phys. 124, 054316 (2006).

Poster Session B B-02

99

Assessing RAFT equilibrium constants through the use of high-level

local correlation methods

João C. A. Oliveira, Ricardo A. Mata

Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstr. 6, Göttingen, Germany

Reversible addition-fragmentation chain transfer (RAFT) polymerization has become one of the most significant methods in the field of radical polymerization. In order to understand the underlying mechanisms, a combination of experiment and theoretical calculations is warranted. However, given the complexity of the systems under study, one will often find disagreements between the two. One possible cause for the disparity can be a different interpretation of the mechanisms, but uncertainty in the experimental measurements or theoretical results can never be excluded. Quantum chemical calculations are particularly challenging in such systems. The molecular sizes can be relatively large (over 20 atoms) and the description of radical species requires the use of high-level electronic structure methods. In this work, we present the application of local correlation methods to the calculation of RAFT equilibrium constants. We focus on two different systems, the addition of the ciano-iso-propyl radical (CIP) to cyano-iso-propyl dithiobenzoate (CPDB) and the addition of the styrene radical (SR) to 1-phenylethyl dithiobenzoate (PEDB). In estimating the equilibrium constants, we have applied local coupled cluster calculations1 in a tailored conjugate method, including basis set extrapolation and solvation effects. In the case of the CPDB system, we were able to obtain remarkable agreement with the experimental value of 9 ± 1 L/mol.2 We also provide an explanation for the discrepancy between the latter value and the previous theoretical works on this RAFT system.3 The accuracy of our conjugate method is further demonstrated in the PEDB reaction. 1. Y. Liu, H.-J. Werner, to be published. 2. W. Meiser, M. Buback, Macromol. Rapid Commun. 32, 1490 (2011). 3. T. Junkers, C. Barner-Kowollik, M. L. Coote, Macromol. Rapid Commun. 32, 1891 (2011).


100

Photoionization of the methylene amidogen radical H2CN and its isomers

F. Holzmeier,a) M. Lang,a) P. Hemberger,b) I. Fischer a)

a) Institute of Physical and Theoretical Chemistry, University of Würzburg, Am Hubland,

97074 Würzburg, Germany b) Molecular Dynamics Group, Paul Scherrer Institut (PSI), 5232 Villigen,Switzerland

The photoionization of the methylene amidogen radical H2CN and its isomers was investigated by imaging photoelectron photoion coincidence (iPEPICO), using VUV synchrotron radiation. Nitrogen-containing radicals are important intermediates in the combustion of bio-fuels and involved in elementary reactions in the interstellar space.1,2 Therefore, the characterization of those species is of great interest. The H2CN radicals were generated by flash pyrolysis from methyl hydrazine as a precursor. At the Swiss Light Source storage ring a mass-selected threshold photoelectron spectrum was obtained. In the spectrum, transitions from all four neutral H2CN isomers (H2CN, cis-HCNH, trans-HCNH, and H2NC) to their respective triplet cation are observed and vibrational bands in the cations could be resolved. This enabled us to determine adiabatic ionization energies for the various isomers. The assignment of the spectral features is backed up by calculated ionization energies and Franck-Condon-simulations. In addition, the transition to a cationic transition state, [H2CN+]#, on the singlet potential energy surface was observed in the threshold photoelectron spectrum.

1. C. U. Morgan, R. A. Beyer, Combust. Flame 36, 99 (1979). 2. P. D. Holtom, C. J. Bennett, Y. Osamura, N. J. Mason, R. I. Kaiser, Astrophys. J. 626, 940 (2005).


101

Infrared Spectroscopy of V+(H2O)n:

Temperature Effects on Isomer Distributions

K. Ohashi,a) J. Sasaki,a) K. Judai,b) N. Nishi,b) H. Sekiya a)

a) Department of Chemistry, Kyushu University, Hakozaki, Fukuoka 812-8581 Japan b) Institute for Molecular Science, Myodaiji, Okazaki 444-8585 Japan

Hydrated metal ions have been the subject of extensive theoretical and experimental research, as such species play important roles in many chemical and biological systems. We have investigated coordination and solvation structures of metal ions through gas-phase IR spectroscopy. We have found that Ar- or N2-tagging of these ions sometimes brings about drastic changes in their IR spectral features, which have been interpreted to be temperature (entropy) effects. In this work, we aim at verifying the interpretation by evaluating thermo-dynamic functions for V+(H2O)n.

The insets of Figure 1 illustrate two isomers of V+(H2O)4: a 4-coordinated (4+0) and a 3-coordinated (3+1) having a second-shell H2O. An IR spectrum of cold ions (recorded with N2-tagging) in the OH stretch region shows only high-frequency bands due to free OH groups, nominating only (4+0) for the candidate.1 Strong and red-shifted bands emerge in a spectrum of warm ions (recorded without N2-tagging), implying a growth of (3+1) with a hydrogen bond between H2O molecules. From ab initio computational results, we calculate partition functions for these isomers under rigid-rotor/harmonic-oscillator approximation. Finally, free energies, G(T), are evaluated for T = 0–2000 K, as shown in Figure 1. (4+0) is lowest in G(T) at low T, which is consistent with the IR spectrum of cold ions. However, (3+1) decline in G(T) with increasing T, which is qualitatively consistent with the IR spectrum of warm ions, although a changeover temperature of Tc = 1350 K is unrealistically high. For V+(H2O)3, (2+1) is higher in G(T) than (3+0) over the entire T range, which is consistent with the IR experiment.

The temperature-dependent spectral changes of V+(H2O)n can be ascribed to entropy effects, although the theoretical treatment needs to be improved for a quantitative agreement.

1. J. Sasaki, K. Ohashi et al., Chem. Phys. Lett. 474, 36 (2009).

Figure 1 Temperature dependence of free energies, relative to (4+0), for two isomers of V+(H2O)4.


102

Intriguing Chemistry of Nitrogen Dioxide Dimers (N2O4)

in cryogenic Matrices

H. Beckers,a) X.-Q. Zeng,a) H. Willner,a) G. A. Argüello b)

a) FB C-Anorganische Chemie, Bergische Universität Wuppertal, Gaussstrasse 20, Wuppertal, Germany

b) INFIQC- Dpto de Físico Química, Fac. de Cs. Qcas., Universidad Nacional de Córdoba, Córdoba, Argentina

The thermal rearrangement of a kinetically stabilized (NO2 )2 radical pair, produced by UV (266 nm) laser photolysis of bis(dioxidonitrogen), O2NNO2 (D2h), have been monitored in various cryogenic matrices (Ne, Ar, O2, N2). Unlike isotropic noble-gas (Ne, Ar) matrices, in which the radical pair decayed with activation energies < 1 kJ mol-1 to yield solely anti ONONO2, weak dipole-quadrupole guest-host interactions in solid molecular oxygen and nitrogen matrices permit a novel syn ONONO2 isomer to be captured at 6 K, and to confirm experimentally the recently predicted multi-step mechanism for this rearrangement (Scheme 1, left).1

Scheme 1: Conversion of a kinetically stabilized (NO2 )2 radical pair (left) and of a matrix-isolated [cis N2O2,O2] complex (right) into anti ONONO2. The 266 nm laser photolysis of O2NNO2 isolated in solid Ar at < 16 K also produced a kinetically stabilized Van-der-Waals complex [syn N2O2,O2].2 The course of the thermal decay of this complex was followed by IR spectroscopy at temperatures between 25 to 33 K (Scheme 1, right). The reaction yields anti ONONO2, and shows an activation barrier of 3.9 0.5 kJ mol-1, which is significantly lower than the gas-phase N N bond dissociation energy of syn N2O2 (8.3 0.05 kJ mol-1). The previously claimed bisnitroso peroxide, ONOONO, was not detected during this low-temperature multi-step conversion.3 1. W. G. Liu, W. A. Goddard III, J. Am. Chem. Soc. 134, 12970 (2012). 2. H. Beckers, X.-Q. Zeng, H. Willner, Chem. Eur. J. 16, 1506 (2010). 3. B. Galliker, R. Kissner, T. Nauser, W. H. Koppenol, Chem. Eur. J. 15, 6161 (2009).


103

Ion-pair formation in the multiphoton photodissociation of HCl studied by

observation of H+ and Cl- ions by 3D-imaging

M. Poretskiy,a) A. I. Chichinin, a,b,c) C. Maul, a) K.-H. Gericke a)

a) Institut für Physikalische und Theoretische Chemie, Technische Universität Braunschweig, Hans-Sommer-Straße 10, 38106 Braunschweig, Germany

b)Institute of Chemical Kinetics and Combustion, Institutskaya,3, Novosibirsk, 630090 Russia

c) Novosibirsk State University, Pirogova Str.,2, Novosibirsk, 630090 Russia

Imaging of positive ions proved to be a very powerful method for the investigation of photodissociation, whereas ion imaging of negative ions has only rarely been used. In contrast to positive ions, negative ions can result only from ion-pair photodissociation channels. Therefore, imaging of negative ions exclusively describes these ion-pair channels.

The purpose of this work is twofold: first, to modify the positive ion imaging setup for simultaneous detection of positive (H+, HCl+, Cl+) and negative ions (Cl-) produced by multi-photon ionization and fragmentation of simple molecules (HCl in the present study) and second, to study the dynamics of the ion-pair formation in the case of HCl. The new imaging setup includes a double-sided time-of-flight mass-spectrometer with 3-dimensional (3D) delay-line detectors1, which are able to determine the velocity of both positive and negative photoions from the same laser pulse:

The HCl ion-pair photodissociation channel starts from a resonant two-photon absorption to an intermediate state IS1. A third photon excites an unknown state IS2, from which we suggest the system to undergo a nonadiabatic transition to the V1Σ+ state, from which the molecule finally dissociates:

HCl (X1Σ+ ) 2h HCl*(IS1) h HCl**(IS2) → HCl**( V1Σ+) → H+ + Cl-. (1)

In our work the 3D velocity distributions of Cl- ions were registered via excitation of IS1= V1Σ+(v = 8,9,10,11,12,13, J = 0), E1Σ+(v = 0, J = 0), and g3Σ-(0+,v = 0, J = 0) states. In all cases, the speed distributions, parameters of anisotropy, and the dependencies of [Cl-] vs squared laser intensity (<I2>) were determined. Such dependencies were obtained for the H+, HCl+, and Cl+ ions also. All observed parameters are close to 2, indicating the symmetry of the state IS2 to be 1Σ+. The dependence of [Cl- ] vs <I2> has a maximum for intermediate values of <I2>. This behavior we explain by the increasing role of the following additional pathway for large laser intensities:

… → HCl**(IS2) →HCl**( V1Σ+) h HCl***(IS3)→ H*(n = 2) + Cl h H+ + e- + Cl, (2)

which reduces the [Cl- ]. The nature of the intermediate states IS1, IS2, and IS3 is discussed. 1. A.I. Chichinin, S.Kauczok,K.-H. Gericke, and C.Maul, Int. Review Phys. Chem. 28, 607 (2009).


104

Laser magnetic resonance study and ab initio calculations for the

O(1D) + VF5 reaction: deactivation and branching ratios

A. A. Rakhymzhan, a) A. I. Chichinin, a,b) V. G. Kiselev, a,b) N. P. Gritsan a,b)

a) Institute of Chemical Kinetics and Combustion, Institutskaya,3, Novosibirsk, 630090 Russia

b) Novosibirsk State University, Pirogova Str.2, Novosibirsk, 630090 Russia The reactions of O(1D) atoms with VF5 at room temperature have been studied by time-resolved laser magnetic resonance (LMR) at the buffer gas (SF6) pressure of 6 Torr1. The O(1D) atoms were produced by the photodissociation of ozone using an excimer laser (KrF, 248 nm). We used SF6 as a buffer gas because it is inefficient in the deactivation of O(1D) atoms, but efficiently quenches vibrational excitation of FO radicals2. VF5 is a highly volative liquid (P=227 Torr at T=300 K), which is used in our group as a convenient photolytic source of fluorine atoms. The absorption cross section of VF5 at 248 nm is 1.6×10-18 cm2, the quantum yield of F atoms is close to unity. The VF4 radicals generated upon photolysis of VF5 are stable and relatively inert species. The most probable channels of the reaction of O(1D) atoms with VF5 are the following:

O(1D)+VF5 1k FO + VF4 , ΔH0

gas=-1.60 eV, (1)

2k 2F(2P) + VF3O, ΔH0gas=-0.62 eV, (2)

3k F2 + VF3O, ΔH0gas=-2.46 eV, (3)

4k O(3P) + VF5, ΔH0gas=-1.96 eV. (4)

By monitoring the kinetics of FO radical formation (in reaction (1) and in the reaction F+O3→FO+O2) the bimolecular rate constant of O(1D) consumption in collisions with VF5 has been determined to be kVF5 = (7.5±2.2)×10-11 cm3/s (kVF5 =k1+k2+k3+k4). The branching ratios for the channels producing FO radicals (k1) and F atoms (k2) have been found to be k1/ kVF5 = 0.11 0.03 and k2/kVF5<0.02, respectively. Quantum chemical calculations at the CCSD(T)/CBS level of theory give evidence that the reactions O(1D) with VF5 proceed via the VF4OF intermediate. The enthalpy of the reaction leading to this intermediate formation was calculated to be -245.8 kJ/mol. In qualitative agreement with the experimental results, the reaction channel O(1D) + VF5 → F +OVF4 (2′) turned out to be 72.9 kJ/mol energetically less favorable than the channel (1) . The dissociation enthalpy of the OVF4 radical was calculated to be very low (18.1 kJ/mol); hence, the decay of OVF4 to F + OVF3 should proceed very fast. The molecular channel (3), though being most favorable thermodynamically, is kinetically unimportant. 1. A. A. Rakhymzhan, A. I. Chichinin, V. G. Kiselev, N. P. Gritsan, J. Phys.Chem., 117, 814 (2013). 2. A. I. Chichinin, L.N.Krasnoperov, Chem. Phys., 143, 281(1990)


105

Decomposition of ortho-, meta-, and para-xylyl radicals in a pyrolysis

reactor: Observation of para-xylylene as product of meta-xylyl dissociation

P. Hemberger,a) A. Trevitt,b) G. da Silva c)

a) Paul Scherrer Institute, Molecular Dynamics Group, Villigen PSI, Switzerland b) School of Chemistry, University of Wollongong, New South Wales 2522, Australia

c) Chemical and Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia

Xylenes (dimethyl benzenes) are applied as petrol additives thanks to their high octane ratings and energy density. The combustion properties of these three isomers (ortho, meta and para) differ strongly, although the first step, the abstraction of an H atom and formation of the corresponding xylyl (methy benzyl) radical, is shared. Shock tube experiments revealed that the decomposition of xylyl radicals to xylylenes differ markedly.1 This motivated us to conduct this study. The xylyl radials were produced in an isomer-selective way from methyl benzylbromide isomer precursors in a Chen-type pyrolysis source,2 heated to up to 1500 K. By increasing the temperature, the radicals can be dissociated by H atom loss to form xylylenes. Soft VUV photoionization with synchrotron radiation and the detection of electrons and ions in coincidence permitted us to measure photoion mass-selected threshold photoelectron spectra (ms-TPES).3 This technique provides an isomer-selective tool to study reactive intermediates and combustion products. Ortho-xylyl radicals (1) show the richest product variety, where two C8H8 species, o-xylylene (2) and benzocyclobutene (3), were identified by modeling their TPE fingerprint (see figure right hand side). Anthracene (4) was detected as a minor reaction product. Apparently, these systems do not only dissociate to closed shell species, but also form polycyclic aromatic hydrocarbons (PAH), the precursors of soot. Both the p-xylyl and m-xylyl radicals decompose to the same product, p-xylylene, by losing a hydrogen atom. In the meta-xylyl radical, a complex rearrangement must precede the formation of p-xylylene. Photoelectron photoion coincidence with VUV synchrotron radiation is used to prove experimentally for the first time that this indeed takes place. 1. R. X. Fernandes, A. Gebert, H. J. Hippler, Proceedings of the Combustion Institute 29, 1337 (2002). 2. D. W. Kohn, H. Clauberg, P. Chen, Rev. Sci. Instrum. 63, 4003 (1992). 3. A. Bodi, M. Johnson, T. Gerber, Z. Gegeliczki, B. Sztaray, T. Baer, Rev. Sci. Instrum. 80, 034101 (2008).


106

Unimolecular Reaction Dynamics of an Imidazolin-2-ylidene: Unraveling

the Complex Dissociation Mechanism of an Arduengo-type Carbene

P. Hemberger,a) A. Bodi,a) T. Gerber a), M. Würtemberger b), U. Radius b)

a) Paul Scherrer Institute, Molecular Dynamics Group, Villigen PSI, Switzerland b) Institute for Inorganic Chemistry, University of Würzburg, Würzburg, Germany

We investigated the photoionization and dissociative photoionization of 1,3-di-iso-propylimidazolin-2-ylidene by imaging photoelectron photoion coincidence (iPEPICO) with VUV synchrotron radiation.1

Propene and methyl radical loss take place in a parallel dissociation only 0.5 eV above the adiabatic ionization energy of 7.52 ± 0.1 eV. The fact that both fragment ions appear at the same photon energy suggests that they share the same rate-determining step. This is also confirmed by quantum chemical calculations, which reveal this step to be hydrogen migration from the isopropyl group to the carbene center forming a resonance stabilized imidazolium ion (see figure).

Analogous sequential dissociation channels open up above 10.5 eV, in which the first propene loss fragment ion dissociates further and another methyl or propene is abstracted. A resonance stabilized imidazolium ion acts again as intermediate for this reaction. The aromaticity of the system is enhanced in vertical ionization, which is the reason for the first exothermic H-migration to generate the imidazolium parent ion with the radical center moved to the side chain. Ab initio methods were used to locate the low-lying transition state for this isomerization step. However, the simple analysis of the breakdown diagram (see figure for excerpt) already yields all the clues to disentangle the complex dissociative photoionization mechanism of this intermediate sized molecule.

iPEPICO is a promising tool to unveil the fragmentation mechanism of larger molecules in mass spectrometry and could thus shed light on the more complex dissociation patterns of organometallic species applied in catalysis. Thermochemical parameters such as bond dissociation energies can be derived from the dissociative photoionization onsets.

1. P. Hemberger, A. Bodi, T. Gerber, M. Würtemberger, U. Radius, Chem. Eur. J. DOI:

10.1002/chem.201204465 (2013).


107

Valence Photoionization Spectra and Absolute Cross-Sections of the

Vinyl, Formyl, and Propargyl Radicals

J. D. Savee, O. Welz, C. A. Taatjes, and D. L. Osborn

Combustion Research Facility, Sandia National Labs, 7011 East Avenue, Livermore, CA, 94550, USA

The vinyl (C2H3), formyl (HCO), and propargyl (C3H3) radicals are transient species commonly found as intermediates in hydrocarbon combustion. Aside from fundamental spectroscopic interests, the valence photoionization behavior of these free-radicals has become increasingly important for their identification in photoionization mass spectrometry experiments aimed at quantitatively understanding the mechanisms by which combustion and atmospherically relevant chemical reactions proceed. For all three radicals photoionization spectra (i.e., photoionization cross-section vs. photon energy) near the first ionization threshold reveal strong features attributed to dynamical autoionizing resonances, which will be discussed in some detail. In the case of the formyl radical, we present measurements of the photoionization spectrum at medium resolution ( 30 meV), revealing vibrational structure from a super-excited state of HCO previously postulated as playing a role in the O + CH reaction.1 The absolute photoionization cross-sections that were determined for each species differ significantly from previously existing values. Although our measurements have been recently confirmed for propargyl,2,3 the discrepancies emphasize the need for multiple independent determinations of this fundamental physical property. Accurate measurements of absolute photoionization cross-sections for small polyatomic free radicals are of particular interest for validation of a recent semi-empirical methodology for predicting photoionization cross-sections by Xu and Pratt.3 Acknowledgment: This work was funded by the Division of Chemical Sciences, Geosciences, and Biosciences, the Office of Basic Energy Sciences, the U. S. Department of Energy. 1. M. MacGregor, and R. S. Berry, J. Phys. B: Atom. Molec. Phys. 6, 181 (1973). 2. J. D. Savee, S. Soorkia, O. Welz, T. M. Selby, C. A. Taatjes, and D. L. Osborn, J. Chem. Phys. 136, 134307

(2012). 3. H. Xu and S. T. Pratt, J. Phys. Chem. A, in press (2013). DOI: 10.1021/jp309874q.


108

Experimental Methods for

Circular Dichroism Laser Mass Spectrometry

D. Jelisavac, K. Titze, C. Logé, U. Boesl

Chemistry Department, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany

Circular dichroism laser mass spectroscopy (CDLAMS) is a new method that can be used as a sensor for chirality in fundamental studies of optically active substances and processes. In this method the substance is ionized with high selectivity and the resulting ions are analyzed with time-of-flight mass spectrometry (TOF-MS). CDLAMS has been used previously to study a number of different chiral molecular systems such as ketones, aromatics and odorous substances and shows good agreement with conventional circular dichroism spectroscopy.

Three experimental methods are used: (1) Double-beam ionization (see figure), (2) so-called twin-peak mass spectroscopy and (3) achiral reference substances. Samples as well as reference substances are introduced into the vacuum via a cannula which emits an effusive gas beam into the ion source of a time-of-flight mass spectrometer. The gas beam is on-axis with the electrode system and thus parallel to the ion flight paths. Laser beam Lb1 is circularly polarized using a quarter-wave plate QW (or a photo-elastic modulator) and is then focused into the effusive gas beam by lens Ll. It passes through the vacuum chamber and is parallelized with a second lens L2. It is then reflected back into the ion source by mirror M and becomes laser beam Lb2. Since the handedness of the polarization is inverted upon reflection at a mirror, laser beam Lb2 exhibits the opposite sense of circular polarization as laser beam Lb1. Lens L2 refocuses laser beam Lb2 into the gas beam. It is placed in such a way that laser beam Lb2 intersects the gas beam at a position several mm upstream. As a result, there exist two spatially separated positions in the ion source where ions are formed. In a specially designed time-of flight mass analyzer two sets of reasonably resolved mass peaks from both positions appear which, however, are shifted in flight time and therefore show up as double peaks (twin peaks) in the mass spectrum. These mass peaks are due to ionization with opposite circular polarized laser light as explained above. In addition, the simultaneously ionized reference substances appear in the same spectrum. All three mass peaks (Ions1, Ions2, achiral reference ions) are therefore formed by the same single laser pulse and thus are subject to the identical laser pulse fluctuations. Measurement of the asymmetry factor g = 2(Ileft – Iright)/(Ileft + Iright) describing circular dichroism via ion currents I thus is much less affected by pulse-to-pulse fluctuations. The same is valid for the corrected g-value gcorr = ganalyte - greference. greference (which should be zero for achiral reference substances) reflects artificial asymmetries of the experiment and allows their correction.


109

Sub-Doppler Electronic Spectra of Benzene Clusters

with Atoms and Small Molecules

M. Hayashi,a) Y. Ohshima a,b)

a) Department of Photo-molecular Science, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, JAPAN

b) School of Physical Sciences, SOKENDAI (The Graduate University for Advanced Studies) Myodaiji, Okazaki 444-8585, JAPAN

Molecular clusters containing a benzene molecule are prototypical systems for elucidating the intermolecular interaction pertinent to aromatic rings. We are now focusing on clusters of benzene attached by small numbers of atoms and molecules, by exploring via two-color R2PI in the vicinity of the monomer S1–S0 60

1 band. We employed a tripled output from a ns pulsed dye amplifier, which was seeded by the CW output from a ring Ti:Sapphire laser, as an excitation source. Owing to the narrow band width (~250 MHz) of the laser system and the efficient rotational cooling down to 0.3 K by implementing a high-pressure pulsed valve, rotational structures have been greatly simplified. Structural parameters of benzene–(He)n with n = 1 and 2 have been substantially refined than those reported previously.1) The distances of He above the plane are set to be: 3.602 (+0.063) Å and 3.596 (+0.057) Å, respectively, where values in parentheses represent the change by the excitation from S0 to S1.2) Several vibronic bands with excitation of intermolecular vibrations have also been observed. The vibronic bands of benzene–He exhibit tunneling splitting due to a large-amplitude migration of He above and below the benzene molecular plane. This finding is matched with the prediction from a high-level ab initio calculation.3) For C6H6–(H2)n, two distinguished isomers, correlating to para and ortho H2, are identified for n = 1 and 2. This finding is the manifestation of the internal rotation of the H2 unit(s) located above (and below) the benzene molecular plane within the complexes. For the observation of the weaker binding para species, a gas sample of pure para H2 was used. Rotationally resolved spectra allowed us to fix the cluster geometry unambiguously. Three vibronic bands involving intermolecular-mode excitation were observed for the ortho species with n = 1, yielding to probable sets of vibrational frequencies of all the three intermolecular modes. One of them correlates to the splitting between the m = 0 and 1 sublevels in the j = 1 state of a freely rotating H2 molecule, and the potential barrier for the hindered internal rotation has been evaluated from the values. Rotationally resolved spectrum of benzene–(ortho H2)3 is consistent with a (2+1) binding motif, where two H2 molecules on one side of the benzene ring seem to scramble their positions and roles. All the complexes examined with rotational resolution exhibited homogenous line broadening, which corresponds to the upper-state lifetimes in the sub-nanosecond regime, most probably due to vibrational predissociation in the S1 61 manifold. We also recorded for the first time rotationally resolved excitation spectrum of the cluster with two Ar atoms lying on the same side of the benzene plane. Excitation specturm of C6H6 –H2O was reinvestigated with much improved resolution than that in the previous report.4) 1. S, M. Beck, M. G. Liverman, D. L. Monts, and R. E. Smalley, J. Chem. Phys. 70, 232 (1979). 2. M. Hayashi and Y. Ohshima, Chem. Phys., in press (2013). 3. S. Lee, J. S. Chung, P. M. Felker, J. L. Cacheiro, B. Fernández, T. B. Pedersen, and H. Koch, J. Chem. Phys. 119, 12956 (2003). 4. A. J. Gotch and T. S. Zwier, J. Chem. Phys. 96, 3388 (1992).


110

Photodissociation Dynamics of the Thiophenoxy Radical at 248 and 193 nm

Aaron W. Harrison,a) Jeong Sik Lim,b) Mikhail Ryazanov, Greg Wang,

Daniel M. Neumark c)

a, c) Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley,

California 94720, USA b) Korea Research Institute of Standards and Science, Daejeon 305-600, Republic of Korea

The photodissociation dynamics of the thiophenoxy radical (C6H5S·) have been investigated using fast beam coincidence translational spectroscopy. Thiophenoxy radicals were produced by photodetachment of the thiophenoxide anion followed by photodissociation at 248 nm (5.0 eV) and 193nm (6.4eV). Experimental results indicate two major competing dissociation channels leading to SH + C6H4· (o-benzyne) and CS + C5H5· (cyclopentadienyl) with a minor contribution of S + C6H5· (phenyl). The SH:CS branching ratio was found to be 0.32:1 (±.05) at 248 nm and 0.92:1 (±.05) at 193 nm. Translational energy distributions were measured for both channels at each wavelength. Potential energy surfaces were calculated using density functional theory to facilitate experimental interpretation. The proposed dissociation mechanism involves internal conversion from the initially prepared excited state to the ground electronic state followed by statistical dissociation. Calculations show that the SH loss channel involves a single isomerization step followed by simple bond fission whereas the CS loss pathway entails multiple transition states and minima as it undergoes bicyclic isomerization followed by five membered ring formation. The calculated surface is consistent with the experimental translational energy distributions in which the CS loss channel has a broader distribution peaking farther away from zero that the corresponding distribution for SH loss.

Figure 1. Translational energy distributions (normalized) of (a) S + C6H5· and (b) CS + C5H5· dissociation channels at 248 (…) and 193 nm (—).


111

Radical chemistry involving ammonia in an astrochemical context.

A step toward prebiotic chemistry?

E. L. Zins, L. Krim

a) Université Pierre et Marie Curie & CNRS - UMR, Laboratoire LADIR, cc 49, 4 place Jussieu, F75 252 Paris Cedex 05, France,

In the context of reactions that may take place in interstellar clouds, ammonia may have played a role as precursor in prebiotic chemistry. Furthermore, in such highly unreactive media, radical chemistry appears as an interesting alternative that may have been involved in the synthesis of organic compounds. As far as astrochemistry is concerned, radical chemistry of ammonia may be split into two kinds of reactions: 1. The first one implies the preliminary formation of amidogen radicals. In molecular clouds,

VUV photolysis may lead to such radicals. Many laboratory experiments aimed at characterizing the photolysis of ammonia. Wide shifts were observed between the solid phase and the gas phase experiments, suggesting the presence of aggregates in solid phase experiments. We attempt to characterize the formation of aggregates between amidogen radical and ammonia during the VUV irradiation of ammonia. To this end Fourier transform infrared (FTIR) spectroscopy was used in combination with the matrix isolation technique in order to characterize species formed during the photolysis of ammonia. The experimental IR spectra were compared with the theoretical frequencies obtained from post Hartree-Fock and DFT calculations for the amidogen radical and its complexes with ammonia molecules. Experimentally, the matrix isolation technique allow us to observe several bands due to the formation of (NH2)(NH3)n complexes. These bands are assigned thanks to the theoretical calculations, and the main results are shown in Figure 1.

Figure 1: Formation of amidogen and (NH2)(NH3)n complexes during the photolysis of ammonia.

2. Alternatively, ammonia may directly react with astrochemically-relevant radicals. In this context, we studied the reactivity between non-energetic OH radicals and ammonia. Among other species, the formation of NH2OH appears as a potentially interesting intermediate toward the synthesis of prebiotic molecules.

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112

Absolute rate coefficient of the gas-phase reaction between

hydroxyl radical (OH) and Hydroxyacetone (HYAC)

Duy N. Vu, Victor Khamaganov, Shaun Carl, Jozef Peeters

Department of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium

Hydroxyacetone is an important tropospheric species and the kinetics of the reaction between HYAC and OH radical have been the subject of several recent investigations.1,2,3,4,5 This presentation reports the experimental determination of rate coefficients for the title reaction over a temperature range (293 - 498 K) and a pressure range (10 - 70 Torr) to elucidate the discrepancy among previous reported rate coefficients and investigate further the mechanism of the reaction. Experiments were conducted using pulsed-laser photolysis coupled to pulsed-laser induced fluorescence (PLP-PLIF). OH radicals were generated by pulsed H2O2 photolysis at 248 nm. The obtained results shows that: at temperatures between 293 - 400 K, at a pressure of 50 Torr, the rate coefficients obeys a negative temperature dependence k = (1.77 ± 0.19) 10 12 exp((353 ± 36)/T) cm3 molecule-1 s-1, which is in good agreement with results of Dillon et al.5 In the temperature range 400 - 498 K, at a pressure of 50 Torr, a positive temperature dependence was found, k = (1.14 ± 0.25) 10 11 exp(-(378 ± 102)/T) cm3 molecule-1 s-1, which is close to the expression obtained by Baasandorj et al.4 for low pressures. Rate coefficients at different pressures (10 -70 Torr) determined at 301 K demostrated a decreasing trend when lowering pressure. The obtained results can be explained using (1) pre-reactive complex model with low barrier energy of transition state, (2) tunnelling effects and collisional relaxation of pre-reactive complex. 1. John J. Orlando, Geoffrey S. Tyndall, Jean-Marc Fracheboud, Edgar G. Estupinan, Sylviane Haberkorn,

Audrey Zimmer, Atmos. Environ., 33, 1621-1629 (1999). 2. Pradyot K. Chowdhury, Hari P. Upadhyaya, Prakash D. Naik, Jai P. Mittal, Chem. Phys. Lett., 351, 201–207

(2002). 3. Nadezhda I. Butkovskaya, Nicolas Pouvesle, Alexander Kukui, Yujing Mu, and Georges Le Bras, J. Phys.

Chem., 110, 6833 - 6843 (2006). 4. Munkhbayar Baasandorj, Stephen Griffith, Sebastien Dusanter, and Philip S. Stevens, J. Phys. Chem., 113,

10495 – 10502 (2009). 5. Terry J. Dillon, Abraham Horowitz, Dirk Ho lscher, John N. Crowley, Luc Vereecken and Jozef Peeters,

Phys. Chem. Chem. Phys., 8, 236 – 246 (2006).


113

Fourier Transform Microwave/Millimeter-wave Spectroscopy of

Metal-Containing Dicarbide Radicals

D. T. Halfen, J. Min, L. M. Ziurys

Departments of Chemistry and Astronomy, Arizona Radio Observatory, Steward Observatory, University of Arizona, Tucson, AZ USA

We have been studying the pure rotational spectra of metal-containing dicarbide radicals, using Fourier transform microwave/millimeter-wave (FTMmmW) spectroscopy in the range 4 – 90 GHz.1,2 The current molecules under investigation are YC2, AlC2, and ScC2.3-5 These species were produced using a Discharge-Assisted Laser Ablation Source (DALAS), which combines laser ablation with a pulsed DC discharge.6 A dilute mixture of methane in argon was used as the precursor gas. Data from 40 – 90 GHz were recorded using newly constructed U-band (40 – 60 GHz) and E-band (60 – 90 GHz) Fourier transform millimeter-wave (FTmmW) systems in the Ziurys group. Metal dicarbide molecules are model systems for heteroatom carbon cluster species, as well as having astrophysical relevance. For YC2 (X2A1), five rotational transitions (N = 1 0 up to N = 5 4) in the Ka = 0 ladder from 10 – 57 GHz have been measured, each exhibiting fine and hyperfine structure due to the yttrium nuclear spin of I(89Y) = 1/2. Spectra from the singly and doubly-substituted carbon-13 isotopologues were also recorded, and an approximate structure was determined, see Ref. 3. For AlC2 (X2A1), three rotational transitions were measured in the range 21 – 65 GHz (N = 1 0, 2 1, and 3 2). Multiple 27Al (I = 5/2) hyperfine components in separate spin doublets were observed. The ScC2 (X2A1) radical has been detected in the gas phase for the first time. Four rotational transitions (N = 1 0, 2 1, 3 2, and 4 3) were measured from 15 – 62 GHz. Both fine and hyperfine (I(45Sc) = 7/2) structure were resolved in these data. Two transitions each of Sc12C13C and Sc13C13C have also been observed and are being analyzed. Rotational, fine structure, and hyperfine constants for these species were determined using an asymmetric top Hamiltonian. The parameters for YC2 and AlC2 are in reasonable agreement with past optical studies, but are more accurate and higher-order constants have been determined. The spectra and rotational constants of these species indicate that they have T-shaped structures, in agreement with theoretical calculations. The carbon-carbon bond length is very similar between molecules, but the metal-carbon bond length and CMC bond angle differ, a likely consequence of the different atomic radii of the metal atoms. From the Fermi contact terms, it was determined that the unpaired electrons in these molecules primarily resides on the metal atom.

1. M. Sun, A. J. Apponi, L. M. Ziurys, J. Chem. Phys. 130, 034309 (2009). 2. D. T. Halfen, J. Min, A. J. Apponi, L. M. Ziurys, in preparation. 3. D. T. Halfen, J. Min, L. M. Ziurys, Chem. Phys. Lett. 555, 31 (2013). 4. D. T. Halfen, J. Min, L. M. Ziurys, in preparation. 5. J. Min, D. T. Halfen, L. M. Ziurys, in preparation. 6. M. Sun, D. T. Halfen, J. Min, B. Harris, D. J. Clouthier, L. M. Ziurys, J. Chem. Phys. 133, 174301 (2009).


114

Pure Rotational Spectroscopy of Chromium-Containing Radicals

J. Min, L. M. Ziurys

Department of Chemistry and Biochemistry, Department of Astronomy,

Steward Observatory, University of Arizona, Tucson, AZ USA We have recorded the pure rotational spectra of CrCCH (X6Σ+) and CrC (X3Σ-), using millimeter/sub-mm direct absorption methods. Both radicals are relevant to transition metal catalysis,1 and the carbide is of astrophysical interest. CrCCH and CrC were created in an AC discharge of Cr(CO)6, acetylene or methane, and argon using the velocity modulation spectrometer of the Ziurys group.2 Ten rotational transitions of CrCCH were measured over the frequency range 250 – 485 GHz; fine structure sextets were resolved in each rotational transition. Five transitions of the isotopic species CrCCD were also measured, confirming the identity of the molecule and its linear structure. The data were analyzed with a Hund’s case (b) Hamiltonian and rotational, spin-spin, and spin-rotation constants determined for both isotopologues. Our parameters for CrCCH are in good agreement with the previous optical study,3 but improve their accuracy; we also have established higher-order fine structure terms. Five rotational transitions of CrC were measured in the frequency range 420 – 580 GHz, each consisting of triplets due to fine-structure interactions, that confirm the X3Σ- ground state. At higher frequency, the splitting between the triplets increases and becomes more asymmetric, resulting from the competition between spin-rotation and spin-spin coupling. The data were fit with a Hund’s case (b) Hamiltonian and rotational, spin-spin and the spin-rotation terms were determined. This study significantly improves the precision of the spectroscopic constants from the previous optical study,4 in particular the fine structure parameters. The bond length of this diatomic radical was found to be r(Cr-C) = 1.631361 Å. Additional measurements of these two radicals using Fourier transform microwave (FTMW) spectroscopy in the frequency range 4 – 85 GHz are currently underway. 1. A. Fürstner, Chem. Rev. 99, 991 (1999). 2. C. Savage, L. M. Ziurys, Rev. Sci. Instrum. 76, 043106 (2005). 3. D. J. Brugh, R. S. Dabell, M. D. Morse, J. Chem. Phys. 121, 12379 (2004). 4. D. J. Brugh, M. D. Morse, A. Kalemos, A. Mavridis, J. Chem. Phys. 133, 034303 (2010).


115

Photodynamics of Triphenylverdazyl radicals in solution

Christoph Weinert, Boris Wezisla, Jörg Lindner, and Peter Vöhringer

Institut für Physikalische und Theoretische Chemie,

Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany

The photochemical and photophysical primary events and the dynamical solute-solvent interactions of open-shell organic molecules in the condensed phase are much less understood than those of closed-shell organic species. This is because carbon, oxygen, or nitrogen-centered radicals are generally highly reactive and their rather short ground state lifetimes preclude a systematic experimental study of the photon-induced dynamics. Verdazyls are a class of open-shell organic compounds that are surprisingly stable by virtue of an extensive delocalization of the spin density across a 1,2,4,5-tetrazine moiety. Here, we studied the non-adiabatic relaxation dynamics of 1,3,5-triphenylverdazyl dissolved in liquid acetonitrile using femtosecond pump-probe spectroscopy with supercontinuum broadband probing. The solute was excited at 800 nm (presumably pumping the D0→D1 transition peaking at 710 nm, HOMO→SOMO transition, cf. Figure left) and at 400 nm (pumping most likely the D0→D2 transition, SOMO→LUMO transition, cf. Figure left). For both excitation wavelengths, the spectro-temporal evolution in the visible (cf. Figure right) suggests that a primary charge transfer from Verdazyl to the solvent intermediately generates Verdazylium cations. Thereby electrons are either transferred to solvent molecules forming solvent radical anions or are released into solvent cavities leading to solvated electrons. The spectro-temporal response is then indicative of charge recombination and decay of the participating transient species on a picosecond time scale.


116

Investigation of Free Radicals from the

Oxidation of -Pinene by Electron Spin Resonance

M.V.Ghosh,a) I. Kuprov,a) P. Ionita b)

a) Department of Chemistry, University of Southampton, Highfield,

Southampton, SO17 1BJ, UK b) Department of Organic Chemistry, University of Bucharest,

Bucharest, 050663, Romania Free radicals control the lifetime of gases important for the Earth’s radiative balance (e.g. CH4), the budget of ozone in all parts of the atmosphere, as well as the production of acidic species. Assessment of the variability of free radical formation from reactions of ozone with terpenes is important for understanding the health effects associated with the particulate matter.1 Studies showed that a significant amount of reactive oxygen species is associated with secondary organic aerosol (SOA) formed under laboratory conditions during the reaction of -pinene with ozone.2 The -pinene oxidation by ozone has been studied in individually levitated aerosol droplets using an acoustic levitator at 100 kHz encased in a custom-built environmental chamber allowing control of the gas-phase surroundings and relative humidity.3 In order to determine the chemical composition of free radical species from the oxidation of levitated -pinene droplets with ozone by Electron Spin Resonance, a spin trap was employed to stabilize the radicals and increase their lifetimes for characterisation.4 The EPR spectra were recorded at ambient temperature on a JEOL FR30EX spectrometer using the following settings: centre field 3360 G, frequency 9.42 GHz, power 4 mW, sweep time 60 s, time constant 0.1 s, modulation frequency 100 kHz and modulation width 1G. The EPR hyperfine coupling constants (due to the interaction of unpaired electron with the nitrogen atom) were extracted from the simulation of the experimental spectra. Hyperfine couplings were also calculated for -pinene-DMPO adduct using DFT B3LYP/EPR-II method in Gaussian 09. An average over 2ps of equilibrated BOMD trajectory was used to account for the vibrational and conformational dependence of hyperfine couplings. Our study demonstrates that it is possible to analyse free radicals by Electron Spin Resonance formed from the oxidation of -pinene in a containerless environment with applications to studies of reaction mechanisms in atmospheric science and beyond. 1. M. Ghosh, S. Almabrok, I. Hoare, D. Stewart, G. Marston, C. Pfrang, European Aerosol Conference

Handbook 12E2, 272 (2011). 2. M. Ghosh, P. Ionita, J McAughey and F. Cunningham, Online J. Org. Chem. ARKIVOC xii, General Papers:

08-2886H (2008). 3. D. Johnson and G. Marston, PCCP 10, 37-39 (2008). 4. J. Pavlovic and P. K. Hopke, Atmos. Chem. Phys. Discuss. 9, 23695-23717 (2009).


117

Rotationally-resolved high-resolution Laser spectroscopy

and the Zeeman effect of the 662 nm band of NO3 B-X transition S. Kasahara,a) K. Tada,a) W. Kashihara,a) M. Baba,b) T. Ishiwata,c) E. Hirota d)

a)Molecular Photoscience Research Center, Kobe University, Kobe, 657-8501, Japan b)Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan

c)Faculty of Information Sciences, Hiroshima City University, Hiroshima 731-3194, Japan d)The Graduate University for Advanced Studies, Kanagawa 240-0193, Japan

The nitrate radical NO3 has been known as an important intermediate in chemical reaction in the night atmosphere.1 The B 2E' ← X 2A2' electronic transition has been known as an intense absorption in the visible region, and the strongest absorption line at 662 nm is called as 0-0 band. The rotational structure of this 0-0 band has been reported by Carter et al.,2 but the rotational assignment is still remained because the spectrum was too complicated to analyze. In this work, rotationally-resolved high-resolution fluorescence excitation spectrum of the 0-0 band of the NO3 B 2E' ← X 2A2' transition has been observed by crossing a single-mode laser beam perpendicular to a collimated molecular beam in the range of 15070-15145 cm-1. NO3 radical was formed by the heat decomposition of N2O5; N2O5 → NO3 + NO2. We have also measured the high-resolution fluorescence excitation spectra of several vibronic bands of the NO2 A 2B2 ← X 2A1 transition which reported in the 15080-15135 cm-1 region,3 and confirmed the NO2 signals were negligibly small compare to the NO3 signals in this region. The typical observed line width was 20 MHz, and the absolute wavenumber was calibrated with accuracy of 0.0001 cm-1 by measurement of the Doppler-free saturation spectrum of iodine molecule and fringe pattern of the stabilized etalon. More than 3000 lines were observed, but it is difficult to assign, except the rotational line pairs from the X 2A2'(υ” = 0, K” = 0, N” = 1, F1 and F2). These pairs have the interval of 0.0246 cm-1 which coincide with the spin-rotation splitting calculated from the molecular constants of the X 2A2' state.4 To confirm these assignment, the Zeeman splittings were also observed up to 360 Gauss. As a results, the transition lines to the B 2E'1/2(υ’ = 0, K’ = 1, J’ = 1/2) and B 2E'3/2(υ’ = 0, K’ = 1, J’ = 3/2) levels were assigned unambiguously from the analysis of the observed Zeeman splittings, and several pairs were found as the same transition in the observed region. Furthermore, we found many small energy shifts in the Zeeman splittings. These results suggest the B 2E'(υ' = 0) state interacts with the other vibronic states. 1. R. P. Wayne, et. al., Atmos. Environ. 25A, 1 (1991). 2. R. T. Carter, K. F. Schmidt, H. Bitto, and J. R. Huber, Chem. Phys. Lett. 257, 297 (1996). 3. R. E. Smalley, L. Wharton, and D. H. Levy, J. Chem. Phys. 63, 4977 (1975). 4. R. Fujimori, N. Shimizu, J. Tang, T. Ishiwata, and K. Kawaguchi, J. Mol. Spectrosc. 283, 10 (2013).


118

Ultrafast pump-probe photoelectron imaging with DUV and VUV pulses

T. Horio,a,b) R. Spesyvtsev,a,b) T. Kobayashi,a) and T. Suzuki a,b)

a) Dept. of Chemistry, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan

b) CREST, JST, Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan

Ultraviolet (UV) and deep UV (DUV) short pulses have been widely employed for time-resolved photoelectron spectroscopy to investigate ultrafast dynamics subsequent to photoexciation of molecules.1-4 However, the photon energies are often insufficient to ionize molecules in low-lying excited states populated by electronic deactivation. In this work, we have demonstrated ultrashort vacuum UV (VUV) pulse generation based on our filamentation four-wave mixing (FWM) light source using neon gas,5 and successfully applied the VUV pulses to pump-probe photoelectron imaging (PEI). The light source is based on a cryogenically cooled Ti:sapphire multipass amplifier system (1.5 mJ, 775 nm, 1 kHz). The fundamental ( , 25 fs, and 0.4 mJ) and its second harmonic (2 , 30 fs, 0.4 mJ) beams were independently focused into neon gas with two concave mirrors (r = 2 m) to initiate filamentation FWM. In addition to DUV pulses of 264 (3 ) and 198 nm (4 ) reported previously,5 VUV pulses at the center wavelength of 157 nm (5 ) have been generated. The pulse energies for 3 , 4 , and 5 were 13, 2, and 0.5 J on source, respectively. The FWM light source was coupled with a three-stage differential pumping system in order that the output DUV and VUV pulses could travel in vacuum to a molecular-beam PEI apparatus. A UV-enhanced aluminum mirror with a drilled hole of 3 mm diameter in the center was used to spatially split the collinearly propagating output beam into two beams for pump-probe experiments: One had a round beam mode (a central part), and the other had a ring-shaped spatial profile (an outter part). The central beam was reflected with dielectric mirrors for 157 nm by 4 times to separate 5 from the other beams ( , 2 , 3 and 4 ). The ring-shaped beam was used for 3 or 4 depending on a molecule studied: We can choose either of the DUV pulses by use of several dielectric mirrors for them. In this poster some experimental results on ultrafast electronic dephasing process such as internal conversion in an isolated molecule are presented, and we discuss about how useful VUV ultrashort pulses are for pump-probe PEI. 1. A. Stolow, A.E. Bragg, and D.M. Neumark, Chem. Rev. 104, 1719 (2004). 2. I. V. Hertel and W. Radloff, Rep. Prog. Phys. 69, 1897 (2006). 3. T. Suzuki, Ann. Rev. Phys. Chem. 57, 555 (2006). 4. T. Suzuki, Int. Rev. Phys. Chem. 31, 265 (2012). 5. T. Fuji, T. Suzuki, E.E. Serebryannikov, and A. Zheltikov, Phys. Rev. A 80, 063822 (2009).


119

Glyoxal Photolysis as a Quantitative Source of HNO

Studied by Frequency Modulation Spectroscopy

N. Faßheber, G. Friedrichs

Institute of Physical Chemistry, Kiel University, Max-Eyth-Str. 1, 24118 Kiel, Germany

Nitroxyl (HNO) is an important intermediate in combustion processes. HNO formation as well as consumption is influenced by a comprehensive radical chemistry. Whereas the HNO oxidation sequence results in the generation of unwanted NOx emission, NOx reduction by CH reburning is initiated by reactions such as CH + NO2 HNO + CO. Using CO as an alternative reburning agent, NOx reduction has been shown to proceed through the reactions H + NO + M HNO + M and HNO + H NH + OH instead.1 Accurate high temperature rate constant data of HNO reactions are needed to optimize combustion processes to prevent NOx formation. Shock tube experiments provide well defined reaction conditions to study high temperature kinetics. Unfortunately, HNO detection behind shock waves is challenging due to its very low absorption cross section and the difficulties associated with generating sufficiently high concentration levels. The combination of 193 nm glyoxal photolysis and sensitive absorption based frequency modulation (FM) spectroscopy2 is a promising way to measure quantitative HNO concentration profiles behind shock waves for the first time. HNO is generated according to (CHO)2 + h H, HCO, H2, CO, CH2O H + (CHO)2 H2 + HCO + CO HCO + NO HNO + CO H + NO + M HNO + M As a prerequisite for high temperature kinetic studies, a detailed assessment of the room temperature gyloxal photolysis and reaction system in the presence of NO has been performed. These experiments allowed us to test the capability and sensitivity of FM spectroscopy to detect HNO on A1A'' - X1A' transitions and to determine the corresponding absorption cross sections by direct comparison of HCO and HNO profiles.

1. P. Glarborg, P. G. Kristensen, K. Dam-Johansen, M. U. Alzueta, A. Millera, and R. Bilbao, Energy Fuels

14, 828-838 (2000). 2. G. Friedrichs, Z. Phys. Chem. 222, 1-30 (2008).


120

The highly anharmonic systems FHF- and ClHCl-:

theory and experiment

P. Sebald,a) A. Bargholz, a) R. Oswald,a) C. Stein,a) P. Botschwina,a) K. Kawaguchi b)

a) Institut für Physikalische Chemie, Universität Göttingen, Tammannstraße 6, D-37077 Göttingen, Germany

b) Department of Chemistry, Okayama University, Tsushimanaka 3-1-1, Okayama 700-8530, Japan

The hydrogen bihalide ions FHF- and ClHCl- are prototypes of highly anharmonic hydrogen-bonded systems with unusual spectroscopic properties. On the basis of very accurate near-equilibrium potential energy and dipole moment functions, obtained from explicitly correlated coupled cluster calculations and fit to a few pieces of precise experimental information, a variety of rovibrational energies and wave functions for different isotopologues of the two anions has been calculated. Theory helped with the assignment of lines observed by IR diode laser spectroscopy in the 1 + 3 combination bands of 35ClH35Cl- and 37ClH35Cl- and enabled to elucidate rather subtle patterns of rovibrational interactions.1 Owing to small differences in the wavenumbers of the proton stretching and bending vibrations, the IR spectra of FHF-, FDF-, and FTF- are characterized by strong Coriolis interaction which is analyzed in detail.2 Many predictions of potential help to forthcoming spectroscopic studies are being made. Accurate bond dissociation energies (D0) are predicted for the three isotopologues of the hydrogen bifluoride ion (in cm-1): D0 (FHF-) = 15176, D0 (FDF-) = 15191, and D0 (FTF-) = 15198. Their accuracy is estimated to be 15 cm-1.3

1. P. Sebald, R. Oswald, P. Botschwina, K. Kawaguchi, Phys. Chem. Chem. Phys. 15, 6737 (2013). 2. P. Sebald, A. Bargholz, R. Oswald, C. Stein, P. Botschwina, J. Phys. Chem. A, (DOI: 10.1021/jp3123677). 3. C. Stein, R. Oswald, P. Sebald, P. Botschwina, H. Stoll, K. A. Peterson, Mol. Phys., in press.


121

Circular Dichroism Laser Mass Spectrometry:

Report of Recent Progress and Outlook to Future Projects

K. Titze, C. Logé, U. Boesl

Chemistry Department, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany

Circular dichroism laser mass spectrometry (CDLAMS) allows enantio-sensitive and mass-selective probing of chiral molecules. It is based on the combination of resonance-enhanced multiphoton ionization (REMPI) with circularly polarized light and time-of-flight mass spectrometry. In conventional circular dichroism spectroscopy the difference in absorption of left and right handed circularly polarized light is measured. In CDLAMS the ion currents I of the respective polarizations are measured. Hence, the asymmetry factor g of a chiral substance can be written as g = 2(Ileft − Iright)/(Ileft + Iright). A validation of the new method is possible by comparing the measured g-factors with gas phase values obtained by conventional circular dichroism spectroscopy. Ongoing development of CDLAMS led to the continuous improvement of the detection limit. Using the twin peak method (specially modified time-of-flight mass spectrometry which involves primary and back reflected laser beams, figure 1) in combination with an achiral reference substance enables measurements of g-values in the per mill range. Hence, CDLAMS is applicable to many classes of chiral molecular systems, e.g. ketones, aromatics and odorous substances.1,2 Furthermore remarkable results were obtained from circular dichroism of molecular ions and two photon circular dichroism.3,4 Latest measurements focus on chiral molecules cooled in a supersonic beam. The cooling of internal molecular motions results in a considerably improved spectral resolution in comparison to room temperature REMPI spectra (figure 2).2 Preliminary circular dichroism measurements in supersonic beams show astonishingly large asymmetry factors. Further experiments will concentrate on molecular clusters of chiral molecules and on chiral substances adsorbed on metal clusters. 1. C. Logé and U. Boesl, Chem. Phys. Chem. 12, 1940 -

1947 (2011). 2. U. Boesl, A. Bornschlegl, C. Logé, K. Titze, Anal.

Bioanal. Chem., submitted 3. C. Logé and U. Boesl, Chem. Phys. Chem. 13, 4218- 4223

(2012). 4. C. Logé and U. Boesl, Phys. Chem. Chem. Phys. 14,

11981 - 11989 (2012).

323 324 325 326 327

ion

curr

ent [

a.u.

]

wavelength [nm]

Figure 1: Twin peak setup of CDLAMS.

Figure 2: REMPI spectrum of 3-methylcyclo-pentanone at room temperature (dotted line) and in a supersonic beam (solid line).


122

High Resolution Laser Spectroscopy of Hafnium Monofluoride

A. G. Adam,a) L. M. Esson,a) A. M. Smith,a) C. Linton,b) and D. W. Tokaryk b)

a) Chemistry Department and Centre for Laser, Atomic and Molecular Sciences, University of New Brunswick, 30 Dineen Dr., Fredericton, NB, Canada E3B 5A3

b) Physics Department and Centre for Laser, Atomic and Molecular Science. University of New Brunswick, 8 Bailey Dr., Fredericton, NB, Canada E3B 5A3

HfF+ is a suitable candidate for making measurements of the electron’s electric dipole moment (EDM).1 Detailed knowledge of the spectrum of neutral HfF is required as an intermediate in preparing HfF+ for EDM experiments. In 2004, our group reported the observation and analysis of several high resolution spectra of HfF in the blue end of the visible spectrum.2 The molecules were produced in a laser-ablation molecular jet source, so the Doppler widths of individual lines were very low (200-300 MHz). In 2012, another group reported the observation of four new bands of HfF in the near infrared,1 with lower resolution than we can achieve. We report here on our follow-up work, in which we have scanned the four near infrared bands at high resolution in our source. One of the bands has a significant perturbation, which was not apparent in the spectra at lower resolution. We have conducted a global fit of the recent work combined with our earlier HfF data (a total of 13 bands) for each of the 180HfF and 178HfF isotopologues, as well as more limited fits for the much weaker 177HfF and 179HfF isotopologues, which have not been previously considered. The results provide an excellent characterization of the ground state and several excited electronic states of HfF. Acknowledment: AGA and DWT acknowledge funding for this project from the Natural Sciences and Engineering Research Council of Canada (NSERC). LME and AMS are grateful recipients of Undergraduate Student Research Assistantships from NSERC. 1. M. Grau, A.E. Leanhardt, H. Loh, L. C. Sinclair, R. P. Stutz, T. S. Yahn, and E. A. Cornell, J. Mol.

Spectrosc. 272, 32-35 (2012). 2. A. G. Adam, W. S. Hopkins, and D. W. Tokaryk, J. Mol. Spectrosc. 225, 1-7 (2004).


123

Experimental and calculated hyperfine structure in the

electronic spectrum of gaseous TaS

Thomas D. Varberg, Andrew J. Bendelsmith, Keith T. Kuwata

Department of Chemistry, Macalester College, 1600 Grand Ave., St. Paul, MN 55105 USA The J (Ω = 5/2)–X1

2∆3/2 (0,0) band at 596 nm and N (Ω = 5/2)–X22∆5/2 (0,0) band at 617 nm of

tantalum sulfide (TaS) were studied by laser excitation spectroscopy. Gas-phase molecules were prepared in a hollow cathode discharge source by the reaction of sputtered tantalum metal with SF6. In order to resolve the hyperfine structure arising from the 181Ta (I = 7/2) nucleus, we recorded sub-Doppler spectra using the method of intermodulated fluorescence (IMF) spectroscopy, resulting in line widths of about 450 MHz. An appropriate Hamiltonian was used to undertake a least-squares fit of the rotational and hyperfine structure, resulting in an accurate set of magnetic dipole and electric quadrupole interaction constants of TaS for the first time. Density functional theory (DFT) calculations were performed on the electronic ground state in order to determine values for the magnetic hyperfine parameters, which agree with the spectroscopically determined values within their experimental error limits.


124

Towards Spin-Orbit Coupled Diabatic Potential Energy Surfaces

for Methyl Iodide Using Effective Relativistic Coupling by Asymptotic Representation

Nils Wittenbrink, Hameth Ndome, and Wolfgang Eisfeld

Fakultät für Chemie, Universität Bielefeld, Bielefeld, Germany

The theoretical treatment of state-state interactions and the development of coupled multidimensional potential energy surfaces (PESs) are of fundamental importance for the theoretical investigation of nonadiabatic processes. Usually, only derivative or vibronic coupling is considered but the presence of heavy atoms in a system can render spin-orbit (SO) coupling important as well. Therefore, we have been developing a new method that allows to compute the SO effects very efficiently and provides a fully coupled diabatic potential energy model.1,2 The method is based on the diabatic asymptotic representation of the molecular fine structure states and an effective relativistic coupling operator. It therefore is called Effective Relativistic Coupling by Asymptotic Representation (ERCAR). In contrast to commonly used simpler approaches, the ERCAR method correctly accounts for the geometry dependence of the SO effects and thus is valid not only in the asymptotic region but also in the strong interaction region. It also is capable to handle allowed and avoided state crossings of all kinds. After testing this approach with a simple diatomic system, we now apply this methodology to generate SO coupled diabatic PESs along the C–I dissociation coordinate for methyl iodide (CH3I). This is the first and mandatory step towards the development of fully coupled full-dimensional PESs to describe the multi-state photodynamics of this benchmark system. This approach allows the efficient and accurate generation of fully coupled PESs including derivative and SO coupling based on high-level ab initio calculations. In the present study we present a specific ERCAR model for CH3I that so far accounts only for the C–I bond cleavage. Further coordinates will be included into the model step by step. Details of the diabatization are given and the accuracy of the results is demonstrated in comparison to reference ab initio calculations and experiments. The energies of the adiabatic fine structure states are reproduced in excellent agreement with ab initio SO-CI data. The model is also compared to available literature data and its performance is evaluated critically. This shows that the new method is very promising for the construction of fully coupled full-dimensional PESs for CH3I to be used in future quantum dynamics studies. 1. H. Ndome, R. Welsch, and W. Eisfeld, J. Chem. Phys. 136, 034103 (2012). 2. H. Ndome and W. Eisfeld, J. Chem. Phys. 137, 064101 (2012).


125

Possible Observation of the 3A’ - 1A’ Electronic Transition of the

Methylene Peroxy Criegee Intermediate Free Radical

Neal D. Kline, Terry A. Miller

Laser Spectroscopy Facility, Department of Chemistry and Biochemistry, The Ohio State

University, 100 W. 18th Avenue, Columbus Ohio, USA Criegee intermediates, which are otherwise known as carbonyl or formaldehyde oxides, are reactive intermediates that are formed in the ozonolysis of olefins in both liquid and gaseous phases. The methylene peroxy intermediate, CH2O2, is formed specifically from the ozonolysis of ethene. In the atmosphere Criegee intermediates are formed in reactions that lead to secondary organic aerosols and participate in reactions with SO2 and NO2. While long postulated to be a key intermediate in these important chemical reactions, the Criegee intermediate had long eluded direct physical detection. Recently Taatjes, et al.,1 Weltz, et al.2

and then Beames, et al.3 reported its detection using mass spectrometry techniques. Earlier this year, Su, et al.4 reported a vibrational spectrum of CH2O2. A peroxy-like electronic spectrum was observed in the near-IR using cavity ringdown spectroscopy by photolyzing a diiodomethane precursor at 248 nm followed by reaction with O2. Possible assignment of the spectrum to CH2O2 is based on a strong analogy between the electronic structure and spectra of methylene peroxy and ozone, in particular the a3A’-X1A’ Wulf bands of O3. However experiments are continuing to positively attribute the spectrum to either CH2O2 or CH2IO2 which could be formed by this chemistry and would also have a spectrum in the near-IR. 1. C. A. Taatjes, G. Meloni, T. M. Selby, A. J. Trevitt, D. L. Osborn, C. J. Percival, D. E. Shallcross, J. Am.

Chem. Soc. 130,11883 (2008). 2. O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Percival, D. E. Shallcross, C. A. Taatjes, Science 335,

204 (2012). 3. J. M. Beames, F. Liu, L. Lu, M. I. Lester, J. Am. Chem. Soc. 134, 20045 (2012). 4. Y.-T. Su, Y.-H. Huang, H. A. Witek, Y.-P. Lee, Science 340, 174 (2013).


126

New Features in the 3D-Applet of the Forthcoming MOGADOC Update

J. Vogt, E. Popov, R. Rudert, and N. Vogt

Chemical Information Systems, University of Ulm, 89069 Ulm, Germany

The MOGADOC database (Molecular GAs-phase DOCumentation) was presented on various symposia of this conference series. In the meantime the database has been grown up to 11,500 inorganic, organic, and organometallic compounds, which were studied in the gas-phase by microwave spectroscopy, radio astronomy, and electron diffraction. The database also contains about 9,000 numerical datasets with internuclear distances, bond angles, and dihedral angles. Most of the corresponding molecular structures are also given as 3D presentation (ball-stick-models).

The retrieval features of the HTML-based database have been described elsewhere in de-tails.1,2 Some years ago a Java-based applet has been developed, which enables the 3D-visualization of the molecular structures. The user can interactively rotate, shift, and scale the 3D-models; moreover one can “measure” bond lengths as well as bond, dihedral and elevation angles.3

Recently new “measurement” features have been supplemented (such as for distances between centroids, angles between ring planes, etc.).

Acknowledgment: The project has been supported by the Dr. Barbara Mez-Starck-Foundation, Freiburg (Germany). 1. J. Vogt, N. Vogt, and R, Kramer, J. Chem. Inform. Comput. Sci. 43, 357 (2003). 2. J. Vogt and N. Vogt, J. Mol. Struct. 695, 237 (2004). 3. N. Vogt, E. Popov, R. Rudert, and J. Vogt, J. Mol. Struct. 978, 201 (2010).


127

PPMODR of Metal Containing Molecules

T. C. Steimle

Department of Chemistry, Arizona State University, Tempe, AZ, USA

The most effective experimental route for probing the nature of a transition metal bonding is from the analysis of high-resolution, gas-phase, spectra that exhibit hyperfine splitting. The nuclei with non-zero spin act as pin-point probes of the electronic wavefunction. The interaction of the unpaired electrons with the nuclear magnetic moment, known as the magnetic hyperfine interaction(MHI), is primarily sensitive to the valence electrons, whereas the interaction nuclear quadrupole moment with the electric field gradient at the sight of the nucleus, known as the nuclear quadrupole interaction (NQI), is sensitive to all the electrons. Since NQI involves an operator prportional to r-3, it is most sensititive to the electronic wave function in the immediate vicinity of the nucleus, which is precisiely where relativisitic effects are most pronounced. The energy shifts and splitting due to NQI (and nuclear spin-rotation) are often two small to be resolved in optical specgtroscopy and require the use of microwave or r.f. spectroscopy. We have applied the sensitive and selective, separated field, pump/probe microwave optical double resonance (PPMODR) to the study the X3 state of WC,1 the X1 state of PtC 2 and, most recentely , the X1 state of RuC. Here will will focus on the interpretation of the NQI paramaters for 101RuC and make a comparision with the scalar relativisitc predictions performed by Prof. Stanton’s group.3

1. C.Qin, R.Zhang, F. Wang and T.C. Steimle, Chem. Phys. Lett. 535,40 (2012). 2 . F. Wang and T. C. Steimle , J. Chem. Phys. 136, 044312 (2012). 3. L. Cheng and J. F. Stanton, private communication.


128

Laser Induced Fluorescence Spectroscopy of Jet Cooled NO3 Free Radicals

Masaru Fukushima and Takashi Ishiwata

Faculty of Information Sciences, Hiroshima City University, Hiroshima 731-3194, Japan

The nitrate free radical, NO3, is one of the simple nitrogen oxides and important intermediates in atmospheric chemistry. In this investigation, we have generated NO3 free radical in supersonic free jet expansion, and observed laser induced fluorescence (LIF) of the B 2E’ – X 2A2’ electronic transition. We have measured the LIF dispersed fluorescence (DF) spectra from the single vibronic levels (SVL) of the 14NO3 and 15NO3 isotopomers. The fluorescent levels of the spectra, i.e. the SVLs, are the 0+0, 0+770, 0+948, 0+1440, and 0+1637 cm-1 and the 0+0, 0+777, 0+925, 0+1435, and 0+1660 cm-1 bands for 14NO3 and 15NO3, respectively. (Since the widths of the vibronic bands are much wider than those of the molecules without Douglas effect, the band positions do not express the vibronic level energy, but the peak of the bands for the measurement of the SVL DF spectra). In the LIF DF spectra, a strong correlation is observed between the two isotopmers (of course, within the isotope shifts). In the LIF DF spectra with our standard resolution (~7 cm-1 in FWHM) obtained by the excitation of the 0+0 cm-1 band, the 1053 cm-1 band of 14NO3 is observed as two bands, 1039 and 1053 cm-1, with an intensity ratio of 4 : 5, respectively, for 15NO3. Higher resolution measurements (~2 cm-1 in FWHM) of the DF spectra show that the 1053 cm-1 band of 14NO3 is also observed as two bands at 1051 and 1056 cm-1 with an intensity ratio of 5 : 3, respectively. The stronger band in spectrum of each species, i.e. the 1051 and 1053 cm-1 band for 14NO3 and 15NO3, respectively, is attributed to be the 1 (a1’) fundamental, because of its little isotope shift, though the isotope shift shows inverse behavior with the usual. There are three possibilities for another band at 1055 and 1038 cm-1 for 14NO3 and 15NO3, respectively, and with the isotope shift of 17 cm-1; (1) the 3 (e’) fundamental band,1 (2) the 2 + 4 (a2’’ and e’, respectively) combination band, and (3) the third over-tone, 3 4, band (a1’, l = 3). If the dominant mechanism is (1), the 3 band should be observed in IR spectrum, but it has yet to be observed. If (2), the intensity must be stolen from the B 2E’ – A 2E’’ transition through the 2 mode, the considerable transition moment of which has been predicted.2 A simple consideration for the vibronic coupling3 between the Ã 2E’’ and X 2A2’ states through the 2 mode may account for approximately 20 % of the combination band intensity to that of the 1 fundamental. If (3), it is unusual that the energy of the 3 4 a1’ level (l = 3) is 120 cm-1 lower than the 3 4 e’ level (l = 1), for the latter of which, the origin is reported to be 1173.629 and 1159.2456 cm-1, for 14NO3 and 15NO3, respectively4 (the 14 cm-1 isotope shift). It is revealed that the 4 vibrational mode of the X 2A2’ state has large an-harmonicity,6,7 which is thought to be caused by vibronic coupling with the B 2E’ electronic excited state through the 4 mode. While the e’ level of 3 4 is affected by the coupling, it is expected to be negligible coupling for the a1’ level because of equivalence of l = 3 with = 0, and to lie at its regular (without perturbation) position, ~1050 cm-1 (= 3 × 350 cm-1). Thus, if the 4 vibronic coupling is possible, (3) can explain the inverse isotope shift of the 1 fundamental level and the isotope shifts of 17 and 14 cm-1 for the 3 4 a1’ and e’ levels, respectively; the 1 level is perturbed by the upper or lower a1’ level of 3 4 for 14NO3 and 15NO3, respectively, and the coupling is about 1 cm-1. 1. J. F. Stanton, J. Chem. Phys. 126, 134309 (2007). 2. J. F. Stanton and M. Okumura, Phys. Chem. Chem. Phys. 11, 4742 (2009). 3. E. Hirota, K. Kawaguchi, T. Ishiwata, and I. Tanaka, J. Chem. Phys. 95, 771 (1991). 4. T. Ishiwata, et al., The 22nd Intl. Conf. on High Resolution Molecular Spectroscopy, paper H24. 5. R. Fujimori, et al., J. Mol. Spectrosc. 283, 10 (2013).


129

Hybrid QM/QM Open-Shell Local Correlation Methods for

the Study of Metal Sites in Biomolecular Catalysis

M . Andrejić, R. A. Mata

Institut für Physikalische Chemie, Universität Göttingen, Tammanstrasse 6, D-37077, Göttingen, Germany

Over one third of all proteins contain at least one metal ion as an essential prosthetic group. For a better understanding of their role in catalysis, computational studies are many a time warranted. The methods used depend on the system under study, but one is usually forced to a hard compromise between accuracy and computational cost. Wave function approaches are often necessary to quantitatively describe these metal centers and their reactivity, although the system sizes can be prohibitive. One further point to the problem is that several of these systems involve open-shell species, which are challenging to handle. The task of treating the aforementioned systems can be, however, somewhat eased. The electronic structure is particularly difficult to describe, but the effects are mostly local (and are regularly connected with the metal centers). In the LMOMO scheme,1 localized orbitals are used to split the system into different regions, treating each at a specific level of theory. This allows for high accuracy in regions where bond breaking/formation takes place, while the remaining environment is described at a low level, thereby reducing the computational cost. Coupled cluster and MP2 approaches can be combined in a single calculation, without resource to model systems.2 We show a first set of applications to open-shell systems, towards the treatment of metallobiosites.

1. R. Mata, H. Werner, M. Schütz, J. Chem. Phys. 128, 144106 (2008). 2. T. Vreven, K. Morokuma, J. Comput. Chem. 21, 1419-1432 (2000).


130

Geminate recombination dynamics of solvated electrons in

liquid-to-supercritical methanol

A. Gehrmann, J. Lindner and P. Vöhringer

Institute for Physical and Theoretical Chemistry, University of Bonn, Wegelerstr. 12, 53115 Bonn, Germany

Solvated electrons can be considered as prototypical radical species. They can be generated in almost any condensed phase material and play a crucial role in electron transfer reactions in fluid media. Since their discovery, solvated electrons have been the subject of numerous experimental and theoretical investigations as they offer a great opportunity to study both solvation and recombination dynamics of a radical and charged particle in solution. We have recently investigated the geminate recombination dynamics of solvated electrons in the liquid-to-supercritical solvents water and ammonia, in order to shed new light on the corresponding ionization mechanisms.1,2 By covering a wide range of temperature and density we were able to correlate the electron´s escape probability from geminate recombination with electronic properties of these two liquids in terms of Onsager´s theory for the initial recombination of ions. In this work we use femtosecond pump-probe-spectroscopy of solvated electrons that were generated by multi-photon ionization of neat liquid-to-supercritical methanol with 266 nm laser pulses. Geminate recombination dynamics were studied over a wide range of temperature (294 K ≤ T ≤ 523 K) and density (5 mol/L ≤ ρ ≤ 25 mol/L) by optically probing the electrons with visible-to-NIR laser pulses. Methanol is the most simple alcohol and less polar than water. Therefore, solvated electrons in methanol allow us to study geminate recombination dynamics in the low permittivity regime of Onsager´s theory. The results are discussed in terms of the thermalization distance of the electrons and their parent molecular fragments.

1. S. Kratz, J. Torres-Alacan, J. Urbanek, J. Lindner, P. Vöhringer, Phys. Chem. Chem. Phys. 12, 12169 (2010). 2. J. Urbanek, A. Dahmen, J. Torres-Alacan, P. Königshoven, J. Lindner, P. Vöhringer, J. Phys. Chem. B 116,

2223 (2012). 3. R. D. Goodwin, J. Phys. Chem. Ref Data 16, 799 (1987).


131

Experimental setup for stereoselective and enantioselective identification

and characterisation of size selected chiral metal cluster catalysts

K. Lange, B. Visser, D. Neuwirth, J. Eckhardt, M. Tschurl, U. Boesl, U. Heiz

Chemistry Department, Technische Universität München, Lichtenbergstrasse 4, Garching, Germany

Size-dependent chemical and physical properties of finite material aggregates are one of the most important investigations in modern science especially with respect to their relevance for heterogeneous catalysis.1

Over several decades the aim of our group has been to control chemical reactions by changing cluster size, chemical composition and dimensionality of metal and metal oxide clusters.2

Thus, it is possible to design cluster catalysts with specified chemical activity, stereo-selectivity and enantioselctivity.3 Chirality is one of the basic principles of nature. It is essential for asymmetric catalytic reactions such as the hydrogenation of β-ketoesters with Ni catalysts4 or the Suzuki-Miyaura coupling reaction which is catalysed by palladium nanoparticles.5 These reactions make use of chiral metal nanoparticles to control the reaction by directing its enantioselectivity. The chiral metal nanoparticles ensure an enantiomeric excess of the product molecule of 90%. The potential for asymmetric catalysis with size selected chiral metal clusters is immense. This work describes the design and construction of a vacuum system to produce, characterise and perform reactions with chiral gas phase metal clusters. The cluster source is of similar design as that used previously within the group.6 It is believed that any population of chiral metal clusters produced within such a cluster source will consist of a racemic mixture of enantiomers. Thus, a method to enable the identification of enantiomers is required. In the current experiment this will be attempted through the introduction of a gas phase enantiopure chiral molecule into the cluster source from a second pulsed nozzle. The added molecule will bind to the metal cluster enantiomers with varying degrees of strength and thus may be probed by either vibrational (REMPI) or dissociation spectroscopy. This presentation will outline the design of the experimental setup and demonstrate the results achieved thus far. 1. A. Baiker, Catalysis Today 100, 159 (2005). 2. A. Sanchez, S. Abbet, U. Heiz, et al., J. Phys. Chem. 103, 9573 (1999). 3. M.Studer, H.-U. Blaser, C. Exner, Adv.Synth.and Catal. 345, 45 (2002). 4. M. Ortega Lorenzo, S. Haq, R. Raval, J. Phys. Chem. B 103, 10661 (1999). 5. H. Fujihara et al., Angew. Chem. Intern. Ed. 47, 6917 (2008). 6. U. Heiz, F. Vanolli, L. Trento, W.-D. Schneider, Rev. Sci. Instrum. 68, 1986 (1997).


132

Use of Antioxidants in Animal Nutrition

A. Díaz-Cruz,a) C. Nava Cuellar,a) A. Martínez García,a) S. Zárate Epstein,a)

J.J. Flores Malpica,a) R. Guinzberg Perrusquía b)

a) Department of Animal Nutrition and Biochemistry, Faculty of Veterinary Medicine and Zootechnics, National Autonomous University of Mexico (UNAM), Mexico City, Mexico

b) Department of Biochemistry, Faculty of Medicine, UNAM, Mexico City, Mexico. An increase in the basal production of free radicals in the cell occurs when oxygen consumption increases. The aim of this study was to identify, under different production systems, oxidant status in broilers, dairy cows and gestating sows through some metabolic indicators of oxidative stress, in order to assess the incorporation of antioxidants in their diet. The results obtained in broilers showed a decrease in levels of TBARS and hydroxyl radicals in broilers liver, and an increase in the concentration of total glutathione in liver, when lipoic acid was incorporated into the diet for a period of 49 days. Furthermore, in a period of 21 days, the zinc in the broilers’ diet decreased in plasma the concentration of TBARS and promoted the increase of the antioxidant activity (FRAP). Regarding dairy cows under a grazing pasture production system, it has been observed that during the transition period, the activity of the enzyme glutathione peroxidase (GSH-Px), and antioxidant activity (FRAP) decrease. Concerning dairy cows in housing, during periparturient, TBARS levels increase and its antioxidant activity (FRAP) decreases. In sows with 45 and 100 days of gestation and at postpartum, the levels of vitamin C showed a time-dependent decrease and the process of plasma protein carbonylation, remains high from 45 days of gestation to postpartum, both indicators compared with non-gestating sows. These data indicate that farm animals, when subjected to a productive requirement, its antioxidant defense system decreases, a metabolic situation that can lead to the development of a state of oxidative stress and eventually lead to a pathological condition, therefore considering the use of antioxidants as prophylactic agents, would be of great benefit to the animal.


133

Free radical products as a biomarker of early Alzheimer´s disease

J. Illner,a) J. Laczo,b) M. Vyhnalek,b) J. Hort,b) A. Skoumalova a)

a) Department of Medical Chemistry and Clinical Biochemistry 2nd Faculty of Medicine

Charles University and University Hospital Motol b) Department of Neurology 2nd Faculty of Medicine Charles University

and University Hospital Motol Alzheimer´s disease (AD) is a neurodegenerative disorder of the brain and the most common form of dementia associated with aging. Pathogenesis of AD is accompanied by overproduction of free radicals in the brain. Moreover, oxidative stress is present in the brain many years before the onset of dementia in the prodromal phase, known as mild cognitive impairment (MCI). Peroxidation of brain polyunsaturated fatty acids results in the formation of lipophilic compounds, lipofuscin-like pigments (LFP), which may diffuse to the blood. It has been hypothesized that oxidative stress in the brain is more pronounced in MCI than in AD dementia. The aim of this study was to analyse LFP in erythrocytes of patients with MCI and compare their amount and composition with those of AD dementia and controls. Fluorescent analyses of LFP characterize the composition of these compounds. Erythrocytes of patient with MCI (n = 25), AD dementia (n = 18) and controls (n = 13) were extracted into chloroform and analyzed by fluorescent spectroscopy. For quantitative analyses tridimensional and synchronous spectral arrays were used. Qualitative differences in the LFP composition in individual patients were studied by second derivations of synchronous spectra and by high pressure liquid chromatography (HPLC). Two pronounced fluorescent maxima 350/440 nm and 290/340 nm (excitation/emission, respectively) were identified by fluorescence spectroscopy. The levels of LFP were significantly increased in the group of MCI (p = 0.01) compared to AD dementia and controls. Qualitative fluorescence analyses revealed seven different fluorophores, which showed a wide variability in quantitative characterization, i.e. the number of LFP (315/340 nm, 310/360 nm) and qualitative characterization, i.e. differences in the composition of LFP (395/420 nm, 390/440 nm) between and within groups. Other qualitative differences in the composition of LFP (310/360 nm, 395/420nm) were identified by HPLC separation. We have found increased amount of LFP in erythrocytes of patients with MCI compared to AD dementia and controls, which might be the result of oxidative stress associated with the pathological changes in the brain in early stages of AD. Fluorescence analyses showed that the composition of LFP in erythrocytes is complex. Acknowledgment: This study was supported by the grant GA UK number 604912.


134

Tea polyphenols act as a central coordinator of oxidative stress,

antioxidants and apoptosis-related mechanism in bleomycin-induced breast cancer cells

Ali A. Alshatwi and Vaiyapuri S. Periasamy

Nanobiotechnology and Molecular Biology Research Laboratory, Department of Food

Science and Nutrition, College of Food and Agricultural Sciences, King Saud University, Riyadh, Kingdom of Saudi Arabia

Bleomycin (BLM), glycopeptide antibiotic-based chemotherapeutic drug, is commonly used to treat various cancers. However, the clinical value of BLM is largely compromised by serious adverse reactions, such as pulmonary fibrosis through oxidative stress. Current breast cancer treatment strategies, primarily mono drug chemotherapy (BLM), result in only minimal improvement in patient survival, and treatments lack specific targeting, thus causing imbalance of oxidative stress. It is well-known that breast cancers are caused by multiple genomic and biochemical alterations. Therefore, therapeutic strategies for breast cancer would require simultaneous use of two or more agents to bring about a synergistic effect than individual drug as well as reduce the toxicity levels. Supplementary antioxidants such as tea polyphenols (TPP) may act as central coordinators of different homoeostatic mechanisms that balance the excessive oxidative stress by various intra-cellular signaling networks. Thus, our research has been focused on the ability of tea compounds, to increase the chemotherapeutic effect on breast cancer cells. Because, tea polyphenols contains epigallocatechin-3-gallate (EGCG), epigallocatechin (EGC), epicatechin-3-gallate (ECG) and catechins, are well known antioxidants that can also inhibit cancer cells through apoptotic mechanism. However, few studies have been conducted on treatments using a combination of TPP and the conventional chemical anticancer drug i.e.BLM. This study was designed to investigate the mechanism of the cytotoxicity of total TPP and BLM, which may synergistically induce cell death in cancer cells. Here, breast cancer cells (MCF-7) were treated with various concentrations of TPP alone or in combination with the chemotherapeutic drug BLM. The effect of TPP on cell growth, intracellular reactive oxygen species (ROS) level, mitochondrial transmentral potential, early apoptosis and gene expression of caspase-3, caspase-8 and caspase-9, Bcl-2, BAX and p53 was investigated. The MTT assay revealed that the MCF-7 cells were less sensitive to growth inhibition by TPP treatment than either BLM or the combination therapy. Propidium iodide nuclear staining indicated that exposure to this combination increased the proportion of apoptotic nuclei compared with a single-agent treatment. Flow cytometry analysis was used to quantify changes in intracellular ROS and mitochondrial trans-membrane potential. Detection of activated caspases by fluorescently labelled inhibitors of caspases (FLICA) combined with the plasma membrane permeability assay demonstrated that the percentage of early and late apoptotic/secondary necrotic cells was higher in the cells treated with the combination than in those treated with either TPP or BLM alone. The combined TPP and BLM treatment synergistically induced apoptosis through caspase-3, caspase-8 and caspase-9 activation, down regulation of Bcl-2 and p53 over-expression. This suggests that TPP plus BLM may be used as an efficient antioxidant-based combination therapy for estrogen receptor (ER)-positive and p53-positive breast cancer.


135

Infrared Detection of Criegee Intermediates formed during the

Ozonolysis of β-Pinene and their Reactivity towards Sulfur Dioxide

J. Ahrens,a) P. T. M. Carlsson,a) M. Pfeifle,b) M. Olzmann,b) T. Zeuch a)

a) Institut für Physikalische Chemie, Universität Göttingen, Tammannstraße 6, 37077 Göttingen

b) Institut für Physikalische Chemie, Karlsruher Institut für Technologie, Kaiserstr. 12, 76131 Karlsruhe

The oxidation of terpenes in the troposhere contributes to the formation of secondary organic aerosol which is known to have a large effect on earth`s climate. However, there is substantial uncertainty about the molecular mechanisms that operate.1 Field observations and experimental studies have shown that the frequency of new particle formation events is correlated to the atmospheric abundance of sulfuric acid (H2SO4). A major source of tropospheric H2SO4 is a reaction sequence that starts with the oxidation of sulfur dioxide (SO2) by the hydroxyl (OH) radical. Another pathway is the oxidation of SO2 to sulfur trioxide (SO3) by the reaction with Criegee intermediates (CIs). CIs are formed during the ozonolysis of alkenes by the decomposition of the primary ozonide (POZ) into the CI and a carbonyl compound or moiety. It was recently shown by direct kinetic measurements that small stabilized Criegee Intermediates (sCIs) react much faster with SO2 than previously assumed.2 These new experiments use a photolytic precursor of sCIs and break the mechanistic connection to the ozonolysis reaction. Here, we show that a direct detection of large sCIs can be achieved within the ozonolysis of biogenic terpenes by taking advantage of characteristic chemical time scales as well as some mechanistic features and IR absorption properties of CIs. Furthermore, we show that refining our earlier approach3 of combining infrared detection of reactants and products with detailed kinetic modelling gives constraints for the sCI + SO2 related kinetic data during β-pinene ozonolysis. In our experiment sCIs are detected by the strong absorption bands of their O-O stretch mode in the 930-830 cm-1 region. Their transient absorption feature appears only in the initial phase of the ozonolysis reaction when scavenging of CIs by carbonyl compounds is less effective. 1. P. Paasonen et al., Nature Geoscience, 6, 438-442, (2013). 2. O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Parcival, D. E. Shallcross, C. A. Taatjes, Science, 335,

204-207 (2012). 3. P. T. M. Carlsson, C. Keunecke, B. C. Krüger, M.-C. Maaß, T. Zeuch, Phys. Chem. Chem. Phys., 14, 15637-

15640, (2012).


136

An Oleic Acid Monolayer Oxidation Study Using Quantitative

Time-Resolved Vibrational Sum Frequency Generation Spectroscopy

Joscha Kleber,a) Kristian Laß,a) Gernot Friedrichs a,b)

a) Institute of Physical Chemistry, Kiel University, Cluster of Excellence “The Future Ocean”, Max-Eyth-Str. 1, D-24118 Kiel, Germany

b) KMS Kiel Marine Science – Centre for Interdisciplinary Marine Science Kiel University, Olshausenstr. 40, D-24098 Kiel, Germany

Natural air-water interfaces including the surface of aqueous aerosols are often covered by a thin film of surface-active organic material, down to monomolecular thickness. These films alter the physical and chemical properties of the interface considerably and, moreover, chemical transformation processes (e.g., atmospheric oxidation, photochemistry) constantly alter the film composition and its physicochemical properties. As an intrinsically surface-sensitive method and with the well-known ozone-oleic acid (OA) heterogeneous reaction system as a test case, we have established vibrational sum frequency generation (VSFG) spectroscopy as a spectroscopic tool to directly study interface kinetics. OA surface concentrations were obtained by careful calibration of spectral intensities relying on combined VSFG/Langmuir trough experiments. Time-resolved VSFG intensity measure-ments enabled the analysis of OA ozone oxidation based on a simple kinetic model. For a monolayer at an air-water interface, the reaction takes place in a protic surrounding such that the Criegee intermediates directly react with water instead of forming the secondary ozonide. No evidence for significant contributions of oxidation products residing at the interface was found that may have interfered with our analysis. A bimolecular rate constant of k(OA + O3

products) = (1.65 ± 0.64) × 1016 cm3 molecules-1 s-1 corresponding to a reactive uptake coefficient of = (4.7 ± 1.8) × 10 6 has been obtained.1 This result is in very good agreement with most recent monolayer measurements based on alternative methods, but is much lower than earlier values reported for pure OA samples, 5 × 10-5 (solid films) < < 7 × 10-3 (pure OA aerosols). This difference stresses the importance of a separate treatment of surface chemistry, diffusion of ozone into the bulk, and secondary bulk phase chemistry.

1. J. Kleber, K. Laß, G. Friedrichs, J. Phys. Chem. A (2013), DOI: 10.1021/jp404087s, in press.


137

Ultrafast electronic deactivation dynamics of hydrogen-bonded self-

assemblies of the 6-oxopurines inosine and guanosine

K. Röttger, F. Temps

Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr.40, 24098 Kiel, Germany

The influence of hydrogen bonding on the electronic deactivation dynamics of nucleobases is a field which is controversially discussed from the experimental as well as the theoretical point of view. Here, the dynamics of hydrogen-bonded self-assemblies of 6-oxopurines in aprotic solvents were investigated using femtosecond time-resolved fluorescence and transient absorption spectroscopy after UV excitation. The results hint at the crucial role of the C(2) position in the six-membered ring for the deactivation pathways of 6-oxopurines. The rare RNA nucleoside inosine in CHCl3, shown in Figure 1, reveals electronic excited state dynamics which are virtually unchanged from the monomer in water1 and are finished on the timescale of ≈100 fs.2 This rapid deactivation is assigned to a barrierless pathway to a conical intersection with the electronic ground state via an out-of-plane deformation of the six-membered ring as is common for 6-oxopurines. The results and the outstanding importance of the C(2) position in the six-membered ring for the deactivation are discussed in comparison with the complex dynamics of guanine monomers in water. Additionally, the results show no evidence for the formation of radical species induced by intermolecular H-transfer or CTTS processes.

Fig. 1. Structure of the inosine dimer in CHCl3. The straightforward results for the inosine dimer form the basis for the discussion of the results obtained for the deactivation of large hydrogen-bonded guanosine ribbons in n-hexane.3 The incorporation into a tight network of guanosine molecules leads to a prodigiously more complex excited-state behavior compared to the G monomer. The results revealed excited-state lifetimes spanning 4 orders of magnitude. This is discussed in terms of energy shifts among the excited states and geometrical constraints, in particular located at the six-membered ring, induced by the hydrogen-bonded network. The intermediate formation of radicals and triplet states that are known as possible photoproducts of guanine will be discussed. 1. K. Röttger, R. Siewertsen, F. Temps, Chem. Phys. Lett. 536, 140 (2012). 2. K. Röttger, F. D. Sönnichsen, F. Temps, Photochem. Photobiol. Sci. accepted (2013). 3. K. Röttger, N. K. Schwalb, F. Temps, J. Chem. Phys. A 117, 2469 (2013).


138

Ultrafast non-radiative dynamics of electronically excited

pentafluorobenzene by femtosecond time-resolved mass spectrometry

O. Hüter, H. Neumann, D. Egorova, F. Temps

Institute of Physical Chemistry, Christian-Albrechts-University of Kiel, Olshausenstr. 40, 24098 Kiel, Germany

The ultrafast non-radiative decay dynamics of jet-cooled, electronically excited pentafluorobenzene were studied using femtosecond transient time-of-flight mass spectrometry. The electronically excited states of the molecule were prepared by femtosecond pump pulses of 30 fs duration and 240–273 nm wavelength, varied in 5 nm steps. The relaxation dynamics were probed by 800 nm, 100 fs pulses in a non-resonant multi-photon ionization process followed by detection of the produced ions with a multi-channel plate assembly. For excitation wavelengths from 240 to 265 nm, the observed temporal profiles exhibit two exponential decay times (τ1 = 2.4 to 14.6 ps and τ2 = 28 to 584 ps). The profiles recorded at 269 nm and 273 nm pump wavelength show five and four decay times, respectively. For the first profile we find τ1 < 0.1 ps, τ2 = 3.97 ps, τ3 = 19.5 ps, τ4 = 337 ps, τ5 > 10 ns, for the latter τ1 < 0.1 ps, τ2 = 18.2 ps, τ3 = 290 ps, τ4 = 1526 ps. All time profiles are superimposed by a strong coherent oscillation with 75–78 cm-1 frequency and damping times between 0.8 and 6.0 ps, depending on pump energy. Possible explanations for this behavior could be offered by theoretical work of Mondal and Mahapatra1,2 as well as Egorova.3 Their quantum-chemical calculations indicate that the fivefold fluorine substitution significantly lowers the energy of the πσ* electronic state localized on the C–F bond, becoming the S2 state after the S1 state of ππ* character. This leads to a low-lying conical intersection as well as a strong vibronic coupling between these states. The consideration of the ionic state D0 reached through the probe pulse in the calculations and an interpretation of the observed decay dynamics in the context of these findings is still ongoing. 1. T. Mondal and S. Mahapatra, J. Chem. Phys. 133, 084304 (2010). 2. T. Mondal and S. Mahapatra, J. Chem. Phys. 133, 084305 (2010). 3. D. Egorova, unpublished results.


139

A New Continuous-Wave Infrared Stimulated Emission Experiment

beyond the Doppler Limit

M. Siltanen,a) M. Metsälä,a) M. Vainio,a,b) L. Halonen a)

a) Department of Chemistry, University of Helsinki, Helsinki FIN-00014, Finland b) Centre for Metrology and Accreditation, Espoo FIN-02151, Finland

We present a sensitive experimental method for molecular spectroscopy that can be used to determine ro-vibrational states using mid-infrared stimulated emission. Our infrared stimulated emission probing (IRSEP) experiment is based on using a narrow-line, continuous-wave Ti:sapphire laser beam (pump) to excite the molecules to an upper vibrational state and a continuous-wave, mid-infrared beam from an optical parametric oscillator (probe) to detect the stimulated emission by the excited molecules. Spectroscopic data are gathered by tuning the wavelengths of the beams. The molecules are probed before their velocity distribution is disturbed by collisions, which leads to a sub-Doppler resolution and full width at half maximum of the emission peaks below 10 MHz. The stimulated emission lines are measured with an accuracy of at least 0.005 cm−1. We use the IRSEP experiment to observe and analyze the symmetric ro-vibrational state [21+] (3ν1(Σg)) of acetylene (C2H2). This state is not accessible via one photon transitions from the ground vibrational state. We use the least-squares method to determine that the band center is at 9991.9725 (12) cm-1 and the rotational parameters are B = 1.156145 (22) and D = 1.608 (87) ×10-6 cm-1, where the uncertainties in parentheses are one-standard errors in the least significant digit.


140

Characterization of high pressure supersonic plasma source: hollow cathode effect in direct current high pressure slit jet micro-discharge

O.Votava,a) P.Pracna,a) M. Mašát,a,b) V. Svoboda,a,c) and M. Fárník a)

a) J. Heyrovský Institute of Physical Chemistry, ASCR, Dolejškova 3, Prague 8,

Czech Republic b) Institute of Organic Chemistry and Biochemistry, ASCR, Flemingovo nám. 2, Prague 6

Czech Republic c) Institute of Chemical Technology Prague, Technická 1905/5, Prague 6, Czech Republic

We present a detailed characterization of a supersonic plasma source for cold molecular radicals direct absorption spectroscopic studies. The radicals are created in a high pressure DC electric discharge and cooled by subsequent supersonic expansion through a slit nozzle. Absorption spectroscopy in the near IR region is used to probe the neutral transient species formed in the discharge, using tunable extended cavity diode lasers. In helium expansion we observe two distinct modes of the discharge that differ by both the electrical characteristics and radical production efficiency, in dependence on the stagnation pressure. Those discharge modes exhibit dramatically different plasma chemistry, specifically we observe significantly (< 10 ) lower yield of OH radicals produced from H2O precursor in the high pressure (P0 > 300Torr) mode compared to the low pressure mode (P0 < 300Torr). To describe this unexpected behavior of the radical source we have performed detailed measurements of the current-voltage characteristics, and spectroscopic measurements of OH radical concentrations and temperatures for both the low and high pressure regimes. Based on the experimental data and model calculations of electric field inside the discharge cavity we show that the observed mode transition is related to hollow cathode effect in the exit slit. This effect leads to localization of the discharge to very small volume near the jet-limiting orifice, rather than in the inter-electrode volume. Low radical concentrations in the high pressure regime are consistent with the reduced time the precursor molecules are exposed to the discharge. Acknowledgment: Support of the Grant Agency of the Czech Republic project No.: 13-11635S is acknowledged.

141

Index

Abrash, Samuel A., Dr. Abstract A17

Adam, Allan G., Prof. Abstract A9, B25

Adam, Max Gerrit Abstract A37

Alcaraz, Christian, Dr. Abstract H4

Alexander, Millard H., Prof. Abstract I15

Alshatwi, Ali A., Prof. Abstract B37

Andrejić, Milica Abstract B32

Azyazov, Valeriy, Dr. Abstract A20

Baklanov, Alexey V., Prof. Abstract A6

Banerjee, Agniva Abstract A36

Beckers, Helmut, Dr. Abstracts A21, B5 & Session II

Berestneva, Yulia Abstract A12

Berresheim, Harald, Prof. Abstract A37 & Session V

Bieske, Evan J., Prof. Abstract H7

Botschwina, Peter, Prof. Abstracts A26, B23

Buback, Michael, Prof. Abstract I12

Butler, Laurie J., Prof. Abstract I8

Casavecchia, Piergiorgio, Prof. Abstracts I7, A11

Chandler, David, Dr. Session IV

Cheung, Allan S.C., Prof. Abstract A15

Chichinin, Alexey I., Prof. Abstracts A14, B6, B7

Continetti, Robert E., Prof. Abstract A4 & Session VII

Díaz-Cruz, Antonio, Dr. Abstract B35

Eisfeld, Wolfgang, Dr. Abstract B27 & Session VIII

Ellison, Barney, Prof. Abstract I10

Endo, Yasuki, Prof. Abstract A31

Ernst, Wolfgang E., Prof. Abstract I4

Eskola, Arkke J., Dr. Abstracts H10/A43, A39

Faßheber, Nancy Abstracts H11, B22

Fischer, Ingo, Prof. Abstracts H12, A5, B4

Fittschen, Christa M., Dr. Abstracts I9, A24

Friedrichs, Gernot, Prof. Abstracts H11, B22, B39

Fukushima, Masaru, Prof. Abstract B31

Gehrmann, Annika Abstract B33

Ghosh, Mariana V., Dr. Abstract B19

Giegerich, Jens Abstract A5

Goulay, Fabien, Dr. Abstract A8

Grabow, Jens-Uwe, Prof. Abstract H6

Index

142

Halfen, DeWayne T., Dr. Abstract B16

Halonen, Lauri, Prof. Abstract B42, Session III

Harrison, Aaron W. Abstract B13

Hemberger, Patrick, Dr. Abstracts I21, B3, B8, B9

Hirota, Eizi, Prof. Abstracts H8, B20

Holz, Mathias Abstract A36

Holzmeier, Fabian Abstract B3

Horio, Takuya, Dr. Abstract B21

Horke, Daniel, Dr. Abstract B33

Hoshino, Shoma Abstract B22

Hsu, Yen-Chu, Dr. Abstracts A29, A30

Hüter, Ole Abstract B41

Illner, Jan Abstract B36

Jacox, Marilyn E., Dr. Abstract A13

Jelisavac, Dragan, Dr. Abstract B11

Jiménez, Elena, Dr. Abstract A24

Kable, Scott H., Prof. Abstracts I17, H3, A32, A41

Kasahara, Shunji, Dr. Abstract B20

Kasper, Tina, Prof. Abstract I21

Kawaguchi, Kentarou, Prof. Abstracts A44, B23

Klüner, Thorsten, Prof. Abstract I6

Laß, Kristian, Dr. Abstract B39

Leach, Sydney, Dr. Session XI

Lee, Sang K., Prof. Abstract A16

Lee, Yuan-Pern, Prof. Abstracts H2, A2, A25

Lee, Yu-Fang Abstract A2

Linnartz, Harold, Prof. Abstracts I20, A42

Lutter, Volker Abstract A3

Maier, John P., Prof. Abstract A36 & Session XIII

Mata, Ricardo, Prof. Abstracts B2, B32

Mebel, Alexander M., Prof. Abstract A23

Merer, Anthony J., Prof. Abstracts A29, A30 & Session X

Miller, Terry A., Prof. Abstracts H9, B28 & Session I

Moradi, Chris Abstracts A10, B1

O'Connor, Gerard D. Abstracts H3, A32

Ogilvie, J. F., Prof. Abstract A1

Ohashi, Kazuhiko, Prof. Abstract B4

Ohshima, Yasuhiro, Prof. Abstracts A31, B12

Okumura, Mitchio, Prof. Abstract H5

Orr-Ewing, Andrew, Prof. Abstracts I11, A38

Osborn, David, Dr. Abstracts I11, H10/A43, A35, A39, A41, B10

Oswald, Rainer, Dr. Abstracts A26, B23

Pelmenev, Alexander A., Dr. Abstracts A18, A19

Preston, Thomas J., Dr. Abstract A38

Pyryaeva, Alexandra Abstract A6

Röttger, Katharina Abstract B40

Index

143

Romanzin, Claire, Dr. Abstract H4

Savee, John D., Dr. Abstracts H10/A43, I22, A39, B10

Schäfer, Tim, Dr. Abstract A27

Scheer, Adam M., Dr. Abstracts H10/A43, A35

Schmidt, Timothy, Prof. Abstracts H3, A32

Sebald, Peter, Dr. Abstract B23

Sheps, Leonid, Dr. Abstracts A39, A40

Shuman, Nicholas, Dr. Abstract I13

Sims, Ian R., Prof. Abstract I3

Slavíček, Petr, Prof. Abstract H1

Steimle, Timothy C., Prof. Abstracts A9, B30

Suzuki, Toshinori, Prof. Abstracts I19, B21

Temps, Friedrich, Prof. Abstracts A28, B40, B41

Thrun, Alexander Abstract A28

Titze, Katharina Abstracts B11, B24

Tokaryk, Dennis W., Dr. Abstracts A9, B25

Troe, Jürgen, Prof. Abstract I13 & Session VI

Tsukiyama, Koichi, Prof. Abstract A22 & Session IX

Tzeng, Wen-Bih, Prof. Abstract A7

Varberg, Thomas, Prof. Abstract B26

Visser, Bradley, Dr. Abstract B34

Vogt, Jürgen, Dr. Abstract B29

Vöhringer, Peter, Prof. Abstracts I2, B18, B33

Votava, Ondrej, Dr. Abstract B43

Vu, Duy Ngoc Abstract B15

Weinert, Christoph D. Abstract B18

Welz, Oliver, Dr. Abstracts I22, H10/A43, A35, A39, B10

Werner, Hans-Joachim, Prof. Abstract I14

Willner, Helge, Prof. Abstracts A21, B5

Wodtke, Alec M., Prof. Abstracts I5, A27

Wörner, Hans Jakob, Prof. Abstract I1

Yang, Xueming, Prof. Abstract I18

Zeuch, Thomas, Dr. Abstract B38

Zhang, Jingsong, Prof. Abstract I16

Zhao, Dongfeng, Dr. Abstract A42

Zins, Emilie-Laure, Dr. Abstract B14

Ziurys, Lucy M., Prof. Abstracts B16, B17 & Session XII

-- Notes --

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