Electron Driven Reactionsin Free and Bound Molecules

Eugen Illenberger

and coworkers

Institut fuer Chemie und Biochemie

Physikalische und Theoretische Chemie

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Electron driven reactions in molecules

• Ionisation

• Electronic Excitation

e- / hv Free

Coupled to something

• Electron capture

DissociationAutodetachment

ResonantCapture

Dissociative Electron Attachment (DEA)

e- (0 - 10 eV)

M-

X-

RM-

e-

e-

Isolated molecules(effusive molecular beam)

Molecular clusters(supersonic molecular beam)

Adsorbed and condensed molecules (UHV)

20 K

Electron Driven Processes

Subexcitation Energies

• Single molecules (effusive beam)

• Molecular aggregates (supersonic beam expansion)

• Molecular nanofilm (UHV)

• Biomolecular systems

ElectronMonochromator

Molecular Beam

Quadrupole

Faraday CupSkimmer

Detector

Nozzle

ComputerStagnationChamber

Laser (IR, UV)

e- + M M-# R + X-

F-+ SF4NCO

F + SF4NCO-

(103)

(2.5x103)

(2.5x103)

(1)

NCO- + SF5

NCO + SF5-

Tania Oster, EIInt. J. Mass Spectrom. 85 (1988) 125

e- + SF5NCO SF5NCO-#

Judith Langer et al.Phys. Chem. Chem. Phys. 4 (2002) 5105

F3C-CF2I

selective C-I bondcleavage at 0 eV

≈ 10-14 cm2

Direct electronic dissociation

along a repulsive surface

0 105

CF3I- C2F5I-

LUMO: *(C-I)

€

Erot

E*=

1

1+θ

μR2 sin2α

CF3-CF2-IEtrans: 66%

Evib: 19%Erot: 15%

Judith Langer, Stefan Matejcik, EIPCCP 4 (2002) 5105

(CF3)2C=N-N=C(CF3)2)

HFFA

HFFA

Excision of CN-: Multiple bond

cleavages and rearrangement

Ilko Bald, Iwona Dabkowska,Oddur Ingólfsson & EI JCP (2007) 2983

STM

M

e-

Single Molecule Engineering

Selective bond cleavageK.-H. Rieder et al.R. Palmer et al.

Selective vibrational excitationJ. I. Pascual et al.

Scientists from the 's Nanoscale Science Facility have made a breakthrough in manipulating the smallest single molecules and atoms by devising a new technique of molecular dissection which induces the "birth" of a daughter atom from the parent molecule.

This breakthrough, which is highlighted in a paper published in the journal, Nature, today (Thursday 17 March).

The new method, devised by Professor Richard Palmer and Dr Peter Sloan, uses the tip of a Scanning Tunnelling Microscope (STM) to inject two electrons into the parent chlorobenzine molecule to induce a dissociation event - the first electron sets the molecule into vibration and the second electron breaks the bond between the parent molecule and daughter chlorine atom.

e-M

X-

h

Substrate Induced Photochemistry

h

Photoabsorption

Fragment ion desorption (John Polanyi et al.)

Desorption of neutral molecules (Martin Wolf, Gerhard Ertl. et al.

V(z)

Distance Molecule-Surface (z)

M- M

Desorption of Neutrals via ResonancesP. Antoniewicz, Phys. Rev. B21(1980) 388

G. Ertl, M. Wolf et al.

Molecular Aggregates

#mm MMe −− →+

n)M(mMn −+−

Dissociation (DEA)

Collisional stabilization

Van der Waals clusters

Electron induced intra-cluster chemistry

new anionic products

e- + relaxation

Dissociative Associative Attachment

Petra Tegeder, Oddur Ingólfsson et al., Z. Phys. Chem. 195 (1996) 217.

C6F5X

X=Cl, Br, I

Reaction Coordinate Q

Qc

C6F5X

Intracluster Ion-Molecule Reactions

X- + RY [XRY]#- XR + Y-

Nucleophilic Displacement (SN2) Reaction

e.g. : F- + CH3Cl CH3F + Cl-

(Judith Langer)

Binary Clusters (NF3)n• (CH3Cl)m

Judith Langer, Stefan Matejcik & EIPhys. Chem. Chem. Phys. 2 (2000) 1001

DEA to NF3

SN2 Reaction

Electron attachment to CH3COCH3 (A)

Single molecules

[CH3COCH2]¯

= [M¯H]¯

Electron energy / eV

Ion

yiel

d /

s-1 H C

Clusters

Mass / amu

p = 0.25 bar, ε = 0 eV, M: Ar 1:50 with M = CH3COCH3

CH3COCH3 (58 amu) Judith Langer, Isabel Martin & EI

(2007)

Mass spectrum• New dissociative channel at ≈ 0 eV:

Loss of 2 molecules H2

a)from acetone dimer

anion (112 amu)

b)from dimer or trimer

anions forming ion-

molecules-complexes

(170-286 amu)

no M¯

Ion inte

nsi

ty /

arb

itra

ry u

nit

s

Condensed Phase Reactions

• Electron stimulated desorption via DEA(the effect of the medium)

• Slow Electrons as a Soft Tool for Surface Modifications

• Substrate Mediated Processes

Fritz Weik and EI, J. Chem. Phys. 103 (1995) 1406

*

No fragment ion

desorption via DEA

F2C=CF2

CF3I

Gas

CondensedPhase

CPL 296 (1998) 208Surf. Sci. 528 (2003) 67

6 ML

Strong enhancement

CF3-

M

M*

M*-

E

M

M*M*-

0

Free molecule Bound molecule

(ET = 1.5 eV)

Biomolecular Systems

Radiation Damage

Electron driven rections

EA(T-H) ≈ 3 - 4 eV

H. A-Carime, S. Gohlke, EIPRL 92 (2004) 168103

Thymine:

e-+TT-# (T-H)-+ H

DNA Bases

Thymine

PRL 92 (2004) 168103

1

3

6

1.0 eV

1.8 eV

0 1 2 3 4

0

2

4

6

8

10

12

Cro

ss s

ecti

on (

Å2 )

Electron energy (eV)

*

1

3

DB state

Deoxyribose in DNA TAR Ribose

Tetrahydrofuran (THF) as model for the sugar unit in DNA ?

* Resonance Ilko Bald, Janina Kopyra, Iwona DabkowskaEgill Antonsson & EI, JCP 126 (2007) 074308

Electron attachment to the phosphate group

DEA to dibutyl phosphate (DBP)

Constanze König, Janina Kopyra, Ilko Bald & EI Phys. Rev. Letters 97 (2006) 018105

Strand break by single bond cleavage

EIPAM fellow

DEA to dibutyl phosphate (DBP)

EA(PO3) = 4.95 eVEA(PO2) = 3.42 eV

Constanze König, Janina Kopyra, IlkoBald & EI Phys. Rev. Letters 97 (2006) 018105

SSB via excision of P-containing units

R. Barrios, P Skurski and J. Simons, JPC B 106 (2002) 7991

Simons et al. JACS 126 (2004) 6441.

No transfer of excess charge

initially localised on T• H. A.Carime et al., Chem. Phys. Letters 387 (2004) 267.• S. Ptasinska et al., Angew. Chem. Int. Ed. 45 (2006) 183.

1.8 eV

T-A Pairing

1 eV

1.8 eV

HCOOH formic acid

Cluster Experiments(Supersonic beam)

CF3COOH / CF3COOD

+ H

+ HF

+ FCOOH

Isabel Martin et al., CPL 419 (2005) 228

CF3COOH single molecules

Bratislava/Berlin

CF3COOH clusters in themolecular beam

Judith Langer et al., Int. J. Mass Spectrom 249/250 (2006) 477

• strong enhancement of electron capture cross section

• chemical reactions induced at very low energy

• NBs act as antennas for low energy electrons eventually transfer to the backbone (SSB)

• Sugar unit is sensitive

• Phosphate group is sensitive

Different mechanisms contribute to SSBs

Future Directions:

Model DA immobilised on microarrays

Transfer of larger units into the gas phase

Hybridization

Tihomir Solomun et al. Eur. J. Physics D 35 (2005) 437.

Laser induced acoustic desorption (LIAD)(Ilko Bald)

m foil

Pulsed laser (Nd Yag)

Desorbing neutrals

Electrons

Paul Scheier, Tilmann Märk, Universität InnsbruckRoger Azria, Anne Lafossse, Robert Abouaf, Université Paris Sud, Orsay Nigel Mason, UCL London/ Open U. Milton Keynes Stefan Matejcik, Michal Stano, Jan D. Skalny, Comenius University, BratislavaMichael Huels, Léon Sanche, Université de Sherbrooke, QuébecHartmut Hotop, Kaiserslautern /Chris Mayhew, BirminghamE. Krishnakumar, S.V. K. Kumar, Tata Institute, BombayGregorsz Karwasz, Torun/TrentoFranco Gianturco, RomeOddur Ingólfsson, Reykjavik

Sascha Gohlke Janina KopyraRichard Balog Andrzej RosaJudith Langer Iwona DabkowskaEsther Fischbach Constanze KönigIlko Bald Tomas SkalickyIsabel Martin Michal StanoHassan Abdoul-Carime Tihomir SolomunWerner F. Schmidt Jessica ScheikeMario Orzol Marie Perot

FU Berlin

Deutsche Forschungsgemeinschaft (DFG)European Union, ESF (EPIC, COST, EIPAM)

Volkswagen Stiftung

Bundesministerium für Wirtschaft und Arbeit (BMWA)INNOVENT Jena

Alexander-von-Humboldt-StiftungDeutscher Akademischer Austausch Dienst (DAAD)

Freie Universität Berlin

NATO Research Council