Slow electron velocity mapping for the study of cationic states of aromatic molecules CHIH-HSUAN CHANG ¥, GARY V. LOPEZ ¶, PHILIP M. JOHNSON ¶,and TREVOR.

Slow electron velocity mapping for the study of cationic states of

aromatic molecules

CHIH-HSUAN CHANG¥, GARY V. LOPEZ¶, PHILIP M. JOHNSON¶,and TREVOR J. SEARS¥,¶

¥ Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973; ¶ Department of Chemistry, Stony Brook, Stony Brook University, New York 11794

Introduction

Aromatic molecule are benchmark systems for gas phase study.

The substituted group in phenyl structure plays an important role in the spectroscopy and molecular dynamics, such as internal rotation, intersystem crossing, and internal conversion.

The interaction of the electron between the phenyl ring and substituting group.

styrene benzaldehyde phenylacetylenetoluene

p electron molecular orbitals of benzene, toluene, PA, and styrene

-10

-9

4 LUMO+1

LUMO

HOMO

5

4

4

5

4,5

StyrenePAToluene

eV

Benzene

2,3

2

3

HOMO-1

2,3

4,5

1

6

Absorption spectrum of phenylacetylene

180 200 220 240 260 280 300 320

3B21A

1

31A111A

1

21A11A

1

nm

X 500

S1(1B

2)S

0(1A

1)

G. W. King and S. P. So, J. Mol. Spectrosc.37 543(1971)

180 200 220 240 260 280 300 320

1A1

1A1

nm

X 500

1B2

Molecular orbital transition and electronic configuration

35%

1B2 state: 37%(L+1H)+38%(L H-1)1A1 state: 81%(LH)1A1 state:76%(L+1 H-1)

Serrano-Andres et al. J. Chem.Phys 119,4294(2003)

4b1

1b1

2b1

1a2

3b1

2a2

5b1

6b1

HOMO

LUMO

LUMO+1

HOMO-1

37% 38% 36%76%81%

Experimental philosophy for slow electron velocity mapping

S0

S1

D0 IP

0 10 20 30 40 50 60 70 80 90 100 110

pixel

0

90

180

270

0

90

180

270

2=0.46(3)2=0.79(6)

1+1 REMPI scheme1+1’ REMPI scheme

1

1

1

2

F.C. factor

The S1S0 absorption spectrum of jet-cooled PA by 1+1 REMPI

0 200 400 600 800 1000 1200 1400 1600 1800 2000

10b2

18b1121

CC16a1

6a110b1

18a2

CC1

CH1

6b1

CC1121

12

CC118b1

CC1131

CC111

11

CC1

6a1

10b2151151

cm-1

00

0

8

8

71

2

34

15[36]:phenyl CCH,C7C8H8 bend10b[24]:out of plane ring def, C7C8H8 bend6a[12]: C7C8H8 － ring breathβCC[35]: C1C7H8 bendβCH[33]:C7C8H8 bend6b[ 34]: Ring deform1[12]: ring breath

The vibrational levels of phenylacetylene in the S1 stateSymmetry Our result

151 b2 146

10b2 a1 194

10b2151 b2 337

6a1 a1 409

CC1 b2 493

10b16a1 b1 516

6b1 b2 555

CH1 b2 561

CC1151 a1 639

11 a1 719

6a2 a1 821

CC16a1 b2 902

121 a1 945

18a1 a1 954

CC2 a1 917

9a1 a1 1152

131 a1 1191

CC111 b2 1208

6a3 a1 1229

6b111 b2 1271

CC1121 b2 1436

12 a1 1442

CC19a1 a1 146318a16b1 b2 1529

CC19a1 b2 1641

11121 a1 1660

CC1131 b2 1682

1316b1 b2 1754

18a2 a1 1908

CC1 a1 2013

The vibrational levels of phenylacetylene cation in the D0 state via transition of selected levels in the S1 state

-500 0 500 1000 1500

10b2151

6a16a110b1

10b21516a1

6a26a210b1

00 6a1

11

6a2

1110b2

6a2152

11CC1

6a3

CC1 CC16a1 CC16a2CC111

CC110b1

CC1121

(c) CC1

(b) 6a1

(a) 10b2151

Ion internal energy (cm-1)

Vibrational level Vib symmetry Kwon et al. Lin and Tzeng Dyke et al.S1 state

00 151 10b2 10b2151 6a1 CC1 6a110b1 CH1 6b1 11

151 b2 154 150 14310b2 a1 223 221

10b1151 a2 25716a1 a2 346 346

10b2151 b2 3616a1 a1 458 453 449 458 439 460CC1 b2 480 4996b1 b2 572 564 561 560

6a110b1 a2 578151CC1 a1 6486a110b2 a1 685 657

11 a1 748 766 747 7596a110b2151 b2 822

6a2 a1 914 910 904 913 914 9216a1CC1 b2 9391110b2 a1 976

6a210b1 b1 1014 10196a16b1 b2 1044 1024

6a210b2 a1 11076b2 a1 1116

6a1CH1 b2 11196a2152 a1 1185116a1 a1 1216 1205

11CC1 b2 1244 1246CC110a1d b1 1287

116b1 b2 1325 13196a3 a1 1375 1387 1369 1370 1372

6a2CC1 b2 14076a1121 a1 14376a26b1 b2 1471 1474

6a310b1 b1 1475121CC1 b2 1473 1465

12 a1 15146b1121 b2 1517 1538

6a110b1121 b1 15426a310b2 a1 1563

6a26b110b1 a1 1629116a2 a1 166811121 a1 1734126a1 a1 194011131 a1 1994

Summary of vibrational frequencies and their assignment for phenylacetylene in the cation ground state

Angular distribution of electron ionized via different vibration modes

0 1 2 30.00

0.25

0.50

0.75

1.00

combination band with 6an in the ion state

via 6a1 excitation

1 2 30.00

0.25

0.50

0.75

1.00

6an10b1

6an10b2

quantum number (n) in D0 state

via 6a110b1 excitation

)(cos14 2

P

d

d total

Θe-

ε

For a linearly polarized light the angular distribution has the general form:

Summary of the results of PA with SEVM detection

With 1+1 REMPI and slow electron velocity mapping (SEVM) detection, the vibrational structure of S1 and D0 states of the phenylacetylene were determined, as well as the photoelectron angular distribution.

Vibronic coupling with 1A1 state is enhanced by CC in-plane mode.

The 6a, phenyl ring breathing motion, is an active mode in the cation state.

The angular distribution of photoelectron provides vibronic coupling information.