VUV-MATI-PD for Ion Reaction ControlVUV-MATI-PD for Ion Reaction Control

National Creative Research Initiative for Control of Reaction Dynamics National Creative Research Initiative for Control of Reaction Dynamics and School of Chemistry, Seoul National University, Seoul 151-742, Koreaand School of Chemistry, Seoul National University, Seoul 151-742, Korea

Prof. Myung Soo KimProf. Myung Soo Kim

ContentsContents

I.I. Reaction controlReaction control

II.II. Mass-analyzed threshold ionization (MATI) for generation of stMass-analyzed threshold ionization (MATI) for generation of state-selected ion beamate-selected ion beam

III.III. Generation of coherent vacuum ultraviolet (VUV) radiation by fGeneration of coherent vacuum ultraviolet (VUV) radiation by four-wave mixingour-wave mixing

IV.IV. One-photon VUV-MATI spectroscopyOne-photon VUV-MATI spectroscopy

V.V. Photodissociation of conformation-selected 1- CPhotodissociation of conformation-selected 1- C33HH77II+•+•..

VI.VI. SummarySummary

VII.VII. AcknowledgmentsAcknowledgments

I. Reaction ControlI. Reaction Control

A. PerspectiveA. Perspective

One main goal of chemistry – Efficient production of One main goal of chemistry – Efficient production of any useful material as one wishesany useful material as one wishes

Traditional approach – Change T, P, Catalyst, etc.Traditional approach – Change T, P, Catalyst, etc.

Dynamic approach – Utilize dynamic character of a Dynamic approach – Utilize dynamic character of a reaction. For example, change the initial quantum reaction. For example, change the initial quantum state of the reactant system or utilize the special state of the reactant system or utilize the special properties of laser which interacts with the systemproperties of laser which interacts with the system

B. Earlier(1970~1990) attempts on laser control B. Earlier(1970~1990) attempts on laser control of chemical reactions of chemical reactions

Mode Selective ChemistryMode Selective Chemistry

Can we selectively break Y-H bond of X-Y-H by pumping many IR Can we selectively break Y-H bond of X-Y-H by pumping many IR

photons and exciting Y-H stretching vibration, photons and exciting Y-H stretching vibration, (YH)?(YH)?

One of the difficulties – Multiphoton excitation with One of the difficulties – Multiphoton excitation with one IR laser to highly excited one IR laser to highly excited (YH) state is not pos(YH) state is not possible due to anharmonicitysible due to anharmonicity

An alternative – Overtone excitation ( eg, An alternative – Overtone excitation ( eg, =0 → =0 → =10) using tunable dy=10) using tunable dye laser in VISe laser in VIS

=0

2

1

3

45

IVR ( Intramolecular Vibrational Redistribution ) – Main difficultyIVR ( Intramolecular Vibrational Redistribution ) – Main difficulty

Vibrational energy supplied to a particular mode by selective pumping is reVibrational energy supplied to a particular mode by selective pumping is redistributed rapidly to other modes within several psec.distributed rapidly to other modes within several psec.

More or less statistical distribution of internal energyMore or less statistical distribution of internal energy

RRKM-type(statistical) reaction rather than mode-selective reactionRRKM-type(statistical) reaction rather than mode-selective reaction

C. Recent approach – passive and active controlsC. Recent approach – passive and active controls

1.1. Passive control – state-selective chemistryPassive control – state-selective chemistry

Prepare the system close to the path of a particular reactionPrepare the system close to the path of a particular reaction

Vibrational state control of HOD photodissociation – F. Flemming CrimVibrational state control of HOD photodissociation – F. Flemming Crim

Pumping 4 vibrational quanta to Pumping 4 vibrational quanta to (OH) (OH) Y(OD)/Y(OH) ~ 15 Y(OD)/Y(OH) ~ 15

Limited to small systemLimited to small system

IVR is still a problemIVR is still a problem

A+BC

ABC1

2

RAB

RBC

Utilize special properties of laser to manipulate the motionUtilize special properties of laser to manipulate the motionof electrons and nucleiof electrons and nuclei

Brumer-Shapiro schemeBrumer-Shapiro schemeExploits interference between two independentExploits interference between two independentpathways that connect the same initial and final pathways that connect the same initial and final states. states. 33+3 +3 11 most popular most popular

Rice-Tannor-Kosloff-Rabitz schemeRice-Tannor-Kosloff-Rabitz schemePump and dump by femtosecond laser pulses for reaction controlPump and dump by femtosecond laser pulses for reaction controlOptimization of laser pulse shape is thought to be criticalOptimization of laser pulse shape is thought to be critical

2. Active Control2. Active Control

i

f

3

1

1

1

II. Mass-analyzed threshold ionization II. Mass-analyzed threshold ionization (MATI)(MATI)

for generation of state-selected ion beamfor generation of state-selected ion beam

A. Zero electron kinetic energy (ZEKE) spectroscopyA. Zero electron kinetic energy (ZEKE) spectroscopy

1. Outline1. Outline

Step1 – Excite a neutral (M) to a very high Rydberg stateStep1 – Excite a neutral (M) to a very high Rydberg state

Step2 – Ionize it with electric field ( field-ionization)Step2 – Ionize it with electric field ( field-ionization)

Step3 – Detect eStep3 – Detect e-- signal vs. h signal vs. h

High resolution spectrum of MHigh resolution spectrum of M+•+•

2. Rydberg states2. Rydberg states

H-like atom states with one eH-like atom states with one e-- in a high n orbital in a high n orbital

M+•

e-

M+ : Ionic core•e- : Rydberg electron

2)( l

Mnlm n

RE

022 )}

)1(1(

2

11{ a

n

llnr nlm

RM : Mass-dependent Rydberg constant

( R∞ = 109737 cm-1)

: -dependent quantum defect

a0 : Bohr radius (0.529 Å)

StatesStates EEnlmnlm <r><r>nlmnlm

n=200, n=200, =0=0 -3 cm-3 cm-1-1 2 2 mm

n=2000, n=2000, =0=0 -0.003 cm-0.003 cm-1-1 2 mm2 mm

Series of Rydberg states with different n converging to an ionizatiSeries of Rydberg states with different n converging to an ionization limit. Each ionic state has a corresponding Rydberg serieson limit. Each ionic state has a corresponding Rydberg series

Continuum of states ( ionization continuum) is present above eacContinuum of states ( ionization continuum) is present above each ionization threshold.h ionization threshold.

Irradiation with hIrradiation with h shown above shown above Generation of a Rydberg neutral converging to ionic state 2 and MGeneration of a Rydberg neutral converging to ionic state 2 and M

+ •+ • in state 0 or 1 (direct photoionization) in state 0 or 1 (direct photoionization)

Rydberg Series

Ionic state 0

1

2

h

Lifetime of a Rydberg state

∝ ∝nn33

From extrapolation of experimental data of NOFrom extrapolation of experimental data of NO

If we wait for a long time after excitation, only those RydbergIf we wait for a long time after excitation, only those Rydbergstates very close to the ionization threshold will survive.states very close to the ionization threshold will survive.

Then, field-ionization Then, field-ionization High resolution spectrum High resolution spectrum

n=200, p-orbitaln=200, p-orbital = 100 nsec= 100 nsec

n=2000, p-orbitaln=2000, p-orbital = 100 = 100 secsec

3. Field-3. Field-ionizationionization

Pulsed-field ionization(PFI) after a time delayPulsed-field ionization(PFI) after a time delay

Potential energy of Rydberg electron Potential energy of Rydberg electron in the presence of applied field Fin the presence of applied field F

eFrr

eU

4

2

E

U

E(cm-1) ∼4 , F in Vcm-1F

F ,VcmF ,Vcm-1-1 0.010.01 0.10.1 11 100100

E,cmE,cm-1-1 0.40.4 1.31.3 44 4040

nn 500500 300300 170170 5050

Ionization by stray electric fieldIonization by stray electric field

Even with best effort, stray field present in the apparatus > 20 mVcmEven with best effort, stray field present in the apparatus > 20 mVcm -1-1

→ → E = 0.6 cmE = 0.6 cm-1-1

→ → Rydberg states with n > 400 undergo ionization by stray field.Rydberg states with n > 400 undergo ionization by stray field.

It is thought that ZEKE detects Rydberg with n= 200~300 ( 1~3 cmIt is thought that ZEKE detects Rydberg with n= 200~300 ( 1~3 cm -1-1 below th below the ionization thresold) with e ionization thresold) with = 100~300 nsec (?). = 100~300 nsec (?).

4. Removal of direct 4. Removal of direct electronselectrons

Direct electrons : electrons formed by direct PI.Direct electrons : electrons formed by direct PI. Always generated together with Rydbergs.Always generated together with Rydbergs. Must be removed before PFI.Must be removed before PFI.

TechniqueTechnique

Delay PFI until direct electrons are removed by eDelay PFI until direct electrons are removed by e ---e-e-- repulsion or repulsion orby stray field.by stray field.

How much delay?How much delay?

n=200~300 → n=200~300 → =100~200 nsec =100~200 nsecBut, longer delay time, 1~10 But, longer delay time, 1~10 sec, used for ZEKE.sec, used for ZEKE.Namely, Rydberg survive much longer than theoretically expected.Namely, Rydberg survive much longer than theoretically expected.Why?Why?

RRe-

e-

e-

e- e-

e- RR

RR

5. 5. -mixing by Stark effect and ZEKE -mixing by Stark effect and ZEKE statesstates

Rydberg states prepared by photoexcitation → large n, small Rydberg states prepared by photoexcitation → large n, small (∵ ∆(∵ ∆ = = 1)1)

Stark effect by stray field → Stark effect by stray field → -mixing → Relaxation to high -mixing → Relaxation to high states. states.Inhomogeneous field by charged particles → m-mixingInhomogeneous field by charged particles → m-mixing

ZEKE statesZEKE states

High n, High n, , m states, m statesWeak interaction between ionic core and Rydberg eWeak interaction between ionic core and Rydberg e -- ((∵ As ∵ As ↑, <r> ↑). ↑, <r> ↑).Slow autoionization, internal conversion, etc.Slow autoionization, internal conversion, etc.Lifetime lengthened by ~ n.Lifetime lengthened by ~ n.

Eg) n=200 Rydberg state with Eg) n=200 Rydberg state with =1 → =1 → ~ 100 nsec ~ 100 nsec n=200 ZEKE state with high n=200 ZEKE state with high → → ~ 20 ~ 20 secsec

6. ZEKE 6. ZEKE spectroscopyspectroscopy

PFI with 1~10 PFI with 1~10 sec delay after photoexcitationsec delay after photoexcitation

Field-ionization of ZEKE states with n=200~300Field-ionization of ZEKE states with n=200~300

Low voltage electronics for PFI and eLow voltage electronics for PFI and e-- acceleration acceleration

B. Mass-analyzed threshold ionization (MATI)B. Mass-analyzed threshold ionization (MATI)

1. Principle1. Principle

Same as ZEKE.Same as ZEKE.Detects MDetects M+ •+ • generated by PFI, not egenerated by PFI, not e--

Generation of state-selected MGeneration of state-selected M+ •+ • ion beam ion beam

2. Difficulty2. Difficulty Direct ion, MDirect ion, M+ •+ • generated by direct PI, must be removed. Difficult because generated by direct PI, must be removed. Difficult because

mass(Mmass(M+•+•) ≫ mass(e) ≫ mass(e--))

TechniqueTechnique Apply a weak DC field (spoil field,~1VcmApply a weak DC field (spoil field,~1Vcm -1-1) for 1~10 ) for 1~10 sec to remove Msec to remove M+•+•. .

→ Depletion of high n Rydbergs by field-ionization→ Depletion of high n Rydbergs by field-ionization

Since low n Rydbergs are depleted by intramolecular relaxation, Since low n Rydbergs are depleted by intramolecular relaxation, not many Rydbergs are left for PFI.not many Rydbergs are left for PFI.

Poor signal intensity!Poor signal intensity!

3. 3. ,m-mixing by AC field,m-mixing by AC field

Application of a weak AC field (scrambling field) further Application of a weak AC field (scrambling field) further mixes m states → Further lengthening of lifetime.mixes m states → Further lengthening of lifetime.

Regular MATI schemeRegular MATI scheme

Simultaneous pulsing of E2 and E3 voltages needed for Simultaneous pulsing of E2 and E3 voltages needed for time focusing of TOF peaks.time focusing of TOF peaks.

→ → Technically difficult to apply additional AC field.Technically difficult to apply additional AC field.

E1

E2

E31200V

950V

-1V

PFI delay

E3

E2

E1

h M

Photoexcitation

Use of electronic jitterUse of electronic jitter

Switch off E2 voltage just before photoexcitation.Switch off E2 voltage just before photoexcitation.→ → Weak voltage ringing, jitter, serves as scrambling field.Weak voltage ringing, jitter, serves as scrambling field.

E1

E2

E31200V

950V

photoexcitation

PFI delay

0

10000

20000

30000

-10 0 10 20 30 40 50

PFI delay (s)

num

ber

of io

ns

(b) NO+ - MATI w ith scrambling f ield

0

10000

20000

30000

-10 0 10 20 30 40 50

PFI delay (s)

num

ber

of io

ns

(a) NO+ - regular MATI

0

5000

10000

15000

-10 0 10 20 30 40 50

PFI delay (s)

num

ber

of io

ns

(c) NO+ - direct ions

III. Generation of coherent vacuum ultraviolat (VUV) radiIII. Generation of coherent vacuum ultraviolat (VUV) radiation by four-wave mixingation by four-wave mixing

A. Popular photoexcitation scheme for ZEKE/MATIA. Popular photoexcitation scheme for ZEKE/MATI

Two-photon ‘1+1’ Two-photon ‘1+1’

DifficultiesDifficulties

1. Difficult to control multiphoton processes.1. Difficult to control multiphoton processes.

2. Applicable to systems with a stable intermediate state 2. Applicable to systems with a stable intermediate state with E < 220 nm = 5.6 eV.with E < 220 nm = 5.6 eV.

eg. Ceg. C66HH66, IE=9.23 eV, S, IE=9.23 eV, S11-S-S00 = 4.72 eV = 263 nm = 4.72 eV = 263 nm

IE –SIE –S11 = 4.51 eV = 275 nm = 4.51 eV = 275 nm

Most system, SMost system, S11 – S – S00 < 200 nm, diffuse S < 200 nm, diffuse S11..

Two-photon ‘2+1’ is even worse Two-photon ‘2+1’ is even worse

h1

h2

IE

B. One-photon ZEKE/MATI with B. One-photon ZEKE/MATI with VUVVUV

Typical IE = 9~12 eV = 138 ~ 103 nmTypical IE = 9~12 eV = 138 ~ 103 nm

1. VUV generation by four-wave difference frequency mixing in Kr1. VUV generation by four-wave difference frequency mixing in Kr

h1

h2

h3

h4

4p6

5p[5/2]2

5p[1/2]0

h1 = h2 = 212.6nm or 216.7 nm

h3 = 400~800 nm

h4 = 122 ~145 nm, 10 nJ

2. VUV generation by sum frequency mixing 2. VUV generation by sum frequency mixing in Hgin Hg

h1

h2

h3

h4

61S0

71S0 h1 = h2 = 312.8 nm

h4 = 115~125nm

TO

F

MCP

LiF lens

Achromaticlens

UV, S

Temperature-controlledpulsed valve

Hg

Heatingblock

Ar

Water inWater in

Out Out

IV. One-photon VUV-MATI spectroscopyIV. One-photon VUV-MATI spectroscopy

A. ExperimentalA. Experimental

(a) top view

dichroic mirrorKr cellMgF2 lens

photoionization chamber

50cm lens

(b) side view

detector

molecular beam VUVE3

E2E1G

TOF

B. VUV-MATI spectroscopy of 2-iodopropaneB. VUV-MATI spectroscopy of 2-iodopropane

Two ionization thresholds for the ground spin-orbit doublet of 2-CTwo ionization thresholds for the ground spin-orbit doublet of 2-C33HH77II+•+•..

IE(XIE(X11) ~ 9.2 eV = 135 nm = 74000 cm) ~ 9.2 eV = 135 nm = 74000 cm-1-1

IE(XIE(X22) ~ 9.7 eV = 128 nm = 78100 cm) ~ 9.7 eV = 128 nm = 78100 cm-1-1

CC33HH77++ : Dissociation of ionic core of Rydberg neutral : Dissociation of ionic core of Rydberg neutral

Dissociation threshold determinedDissociation threshold determined

e- e-

C3H7I+ C3H7+ + I C3H7

+ + IPFI

Photon energy

CC22HH55II 1-C1-C33HH77II 2-C2-C33HH77II RefRef

IE (XIE (X11))a a

9.3490 9.3490

0.00050.0005

  

9.3492 9.3492 0.0006 0.0006

    

9.35 9.35 0.01 0.01

9.2567 9.2567 0.0005 (G) 0.0005 (G)

9.2718 9.2718 0.0005 (T) 0.0005 (T)

    

9.25 9.25 0.01 0.01

9.26 9.26 0.01 0.01

9.1755 9.1755 0.0005 0.0005

    

9.19 9.19 0.01 0.01

9.18 9.18 0.01 0.01

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19 19 

9 9 

20 20 

IE (XIE (X22))aa 9.9327 9.9327 0.0017 0.0017

  

9.9324 9.9324 0.0006 0.0006

  

  

9.93 9.93 0.01 0.01

9.8332 9.8332 0.0017 (G) 0.0017 (G)

9.8466 9.8466 0.0017 (T) 0.0017 (T)

  

9.84 9.84 0.01 0.01

9.82 9.82 0.01 0.01

9.6903 9.6903 0.0017 0.0017

  

  

9.77 9.77 0.02 0.02

9.75 9.75 0.01 0.01

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19 19 

99

2020

AE(CAE(C33HH77++))

9.8332 9.8332 0.0017 0.0017

  

9.84 9.84 0.01  0.01 

9.8180 9.8180 0.0037 0.0037

9.851 9.851 0.025 0.025

9.77 9.77 0.02 0.02

9.82 9.82 0.01 0.01bb

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1111

99

88

C. VUV-MATI spectroscopy of 1-iodopropaneC. VUV-MATI spectroscopy of 1-iodopropaneIE(XIE(X11) ~ 9.25 eV = 134 nm = 74600 cm) ~ 9.25 eV = 134 nm = 74600 cm- 1- 1

IE(XIE(X22) ~ 9.84 eV = 126 nm = 79400 cm) ~ 9.84 eV = 126 nm = 79400 cm-1-1

Two major peaks in Fig 4 (a)

gauche, 74660 cm-1 anti, 74790 cm-1

D. VUV-MATI spectroscopy of iodobutaneD. VUV-MATI spectroscopy of iodobutane1. iso-Butyl iodide1. iso-Butyl iodide

73972 cm-1 74171 cm-1

2. 2-Iodobutane2. 2-Iodobutane

Conformation assignment not possible

3. 1-Iodobutane3. 1-Iodobutane

Conformation assignment not possible

V. Photodissociation of conformation-selected 1- CV. Photodissociation of conformation-selected 1- C33HH77II+•+•..

A. IntroductionA. Introduction

Gauche and anti ions without any internal energy are formed Gauche and anti ions without any internal energy are formed → → No interconversion between conformersNo interconversion between conformers

Ions prepared under very high vacuum conditionIons prepared under very high vacuum condition → → No collision-induced interconversionNo collision-induced interconversion

For a dissociation occurring faster than interconversion, conformatiFor a dissociation occurring faster than interconversion, conformation-specificity may be observedon-specificity may be observed

→ → Excitation to a repulsive electronic state Excitation to a repulsive electronic state

B. ExperimentalB. Experimental

dichroic mirrorKr cellMgF2 lens

photoionization chamber

50cm lens

photodissociation laser

detector

molecular beam VUVE3

E2E1G

TOF

photodissociation laser

C. Photodissociation TOF profilesC. Photodissociation TOF profiles

1- C1- C33HH77II+•+• C C33HH77++ + I + I ••

TOF profiles of CTOF profiles of C33HH77++ broadened due to kinetic energy release (KER,T) TOF profiles broadened due to kinetic energy release (KER,T) TOF profiles

also affected by polarization of PD laseralso affected by polarization of PD laser → → anisotropic dissociation ( reaction time < rotational period )anisotropic dissociation ( reaction time < rotational period )

T & T & (anisotropy parameter) for gauche > anti (anisotropy parameter) for gauche > antiReaction time < time for interconversion between conformersReaction time < time for interconversion between conformers

607nm

90◦

55◦

35◦

0◦

90◦

0◦

D. Distributions of T D. Distributions of T & &

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.1 0.2 0.3

kinetic energy release, eV

ani

sotr

opy

(a)

(b)

prob

abili

ty

0

10

20

30

GaucheAnti

Distributions of (a) T and (b) obtained by analyzing the TOF profiles of C3H7+

at 607 nm in Fig. 2. The results for the gauche and anti conformations are

shown as the open and filled circles, respectively.

E. <T> & < E. <T> & < > vs internal energy> vs internal energy

Dissociation thresholdDissociation threshold Gauche Gauche ~ 1.3 eV~ 1.3 eV Anti Anti ~ 1.6 eV~ 1.6 eV

0.00

0.05

0.10

0.15

1.0 1.5 2.0 2.5 3.0

photon energy, eV

kine

tic e

nerg

y re

leas

e, e

V (a)

0.0

0.2

0.4

0.6

1.0 1.5 2.0 2.5 3.0

photon energy, eV

anis

otro

py

(b)

(a) <T> and (b) <> vs. photon energy (480 ~ 700 nm) for the photodissociation of C3H7I+ to C3H7

+ + I. The results for the gauche and anti conformations are shown as the open and filled circles, respectively. Some <T> data from the photoelectron-photoion coincidence spectrometric measurement by Brand and coworkers in ref. 7 are shown as open triangles ( ) in (a).∆

F. ThermochemistryF. Thermochemistry

1-C1-C33HH77II+•+• 1- C 1- C33HH77++ + I + I • • ??

1-C1-C33HH77++ is not a stable species! is not a stable species!

2-C2-C33HH77++ and cyclo- Cand cyclo- C33HH77

+ + ( protonated cyclopropane) are stable( protonated cyclopropane) are stable

Four possibilitiesFour possibilities (1) 2-C(1) 2-C33HH77

+ + + I (+ I (22PP3/23/2)) (2) cyclo-C(2) cyclo-C33HH77

++ + I (+ I (22PP3/23/2)) (3) 2-C(3) 2-C33HH77

++ + I (+ I (22PP1/21/2)) (4) cyclo-C(4) cyclo-C33HH77

++ + I (+ I (22PP1/21/2))

Excited state where dissociation occurs is the same for gauche and aExcited state where dissociation occurs is the same for gauche and anti. → Iodine state same.nti. → Iodine state same.

∴ ∴ Either (1) & (2) or (3) & (4)Either (1) & (2) or (3) & (4)

h

Best candidatesBest candidates gauche → 2- Cgauche → 2- C33HH77

++ + I ( + I (22PP1/21/2)) anti → cyclo- Canti → cyclo- C33HH77

+ + +I (+I (22PP1/21/2))

00, KfH

00KH 0

0KHSystemSystem ((eV)eV)†† , , gauchegauche (eV) (eV) , , antianti (eV) (eV)

ReactantReactant

1-C1-C33HH77II++((gauchegauche)) 9.170 9.170

0.0400.040

1-C1-C33HH77II++ ( (antianti)) 9.186 9.186

0.0400.040ProductProduct

2-C2-C33HH77++ + I ( + I (22PP3/23/2)) 9.627 9.627

0.0390.039 0.457 0.457 0.056 0.056 0.442 0.442 0.056 0.056

cc-C-C33HH77++ + I ( + I (22PP3/23/2)) 9.958 9.958

0.0410.041 0.788 0.788 0.056 0.056 0.772 0.772 0.056 0.056

2-C2-C33HH77++ + I ( + I (22PP1/21/2)) 10.570 10.570

0.0390.039 1.400 1.400 0.056 0.056 1.385 1.385 0.056 0.056

cc-C-C33HH77++ + I ( + I (22PP1/21/2)) 10.901 10.901

0.0410.041 1.730 1.730 0.056 0.056 1.715 1.715 0.056 0.056

† Enthalpy of formation at 0 K. For products, it is the sum of the two. Data for the reactants and 2-C3H7+ (8.517 eV) are

evaluated with thermochemical data in ref. 6 and ref. 22. Enthalpy of formation at 0 K of c-C3H7+, 8.847 eV, is evaluate

d using the ab initio results at the G2 level. The energy difference between the two fragment ions, 0.331 eV, is close to the ab initio result, 0.313 eV, at the MP4/6-311G** level, ref. 16. Using the enthalpy of formation of c-C3H7

+ obtained from the proton affinity measurement in ref. 23, 8.864 eV, the experimental difference becomes 0.347 eV, which is in decent agreement with the G2 result. Enthalpies of formation at 0 K of I (2P3/2) and I (2P1/2) are 1.1107 and 2.0534 eV, respectively, ref. 24.

G. Ab initio calculationG. Ab initio calculation

Intramolecular SIntramolecular SNN2-type rearrangement accompanies the 2-type rearrangement accompanies the

C-I bond breaking, both for gauche and anti.C-I bond breaking, both for gauche and anti.

Potential energy along the reaction path. Changes in potential energies along the minimum energy paths for the dissociations of gauche and anti isomers in the first excited state were obtained by ab initio calculation at the CIS level. The 6-31G** basis set was used for carbons and hydrogens, while the LanL2DZ basis set was used for iodine. Equilibrium geometries of the gauche and anti isomers in the ground electronic state at the Hartree-Fock level were taken as the initial geometries of the photoexcited 1-C3H7I+. Then, the energies and gradients in the first excited state corresponding to the above configurations were calculated by CIS. Finally, the minimum energy paths from these configurations were calculated by the steepest descent method. The energy of the products, 2-C3H7

+ + I, is taken as the zero of the energy scale. Some representative geometries are also drawn.

VI. SummaryVI. Summary

A. VUV-MATI useful to obtain accurate ionization energies to the groA. VUV-MATI useful to obtain accurate ionization energies to the ground and some excited electronic states, vibrational frequencies, und and some excited electronic states, vibrational frequencies, dissociation thresholds.dissociation thresholds.

B. Conformation-selected ion beam generated for haloalkane ionsB. Conformation-selected ion beam generated for haloalkane ions

C. Conformation-specific reaction observed for the first time. It has C. Conformation-specific reaction observed for the first time. It has been clearly demonstrated that conformation can be gateways to been clearly demonstrated that conformation can be gateways to different reactions as has been long postulated in stereochemistdifferent reactions as has been long postulated in stereochemistryry

D. Conformation-specificity, a well-known concept in chemistry, can D. Conformation-specificity, a well-known concept in chemistry, can be a useful alternative to more elaborate control schemes presebe a useful alternative to more elaborate control schemes presented so far.nted so far.

VII. AcknowledgmentsVII. Acknowledgments

This work was supported financially by CRI, the ministry of SciencThis work was supported financially by CRI, the ministry of Science and Technology, Republic of Korea.e and Technology, Republic of Korea.

ParticipantsParticipants

Prof. Hong Lae Kim , Kangwon National Univ.Prof. Hong Lae Kim , Kangwon National Univ. Prof. Sang Kyu Kim , Inha Univ.Prof. Sang Kyu Kim , Inha Univ. Dr. Wan Goo HwangDr. Wan Goo Hwang Dr. Sang Tae ParkDr. Sang Tae Park Chan Ho Kwon Chan Ho Kwon