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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.