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 benzaldehydephenylacetylene toluene

 electron molecular orbitals of benzene, toluene, PA, and styrene  2,3  4,5 11 66

Absorption spectrum of phenylacetylene G. W. King and S. P. So, J. Mol. Spectrosc (1971)

Molecular orbital transition and electronic configuration 35% 1 B 2 state: 37%(L+1  H)+38%(L  H-1) 1 A 1 state: 81%(L  H) 1 A 1 state:76%(L+1  H-1) Serrano-Andres et al. J. Chem.Phys 119,4294(2003)

Experimental philosophy for slow electron velocity mapping S0S0 S1S1 D0D0 IP  2 =0.46(3)  2 =0.79(6) 1+1 REMPI scheme 1+1’ REMPI scheme F.C. factor

The S 1  S 0 absorption spectrum of jet-cooled PA by 1+1 REMPI [ 36 ]:phenyl CCH,C 7 C 8 H 8 bend 10b[ 24 ]:out of plane ring def, C 7 C 8 H 8 bend 6a[ 12 ]: C 7 C 8 H 8 － ring breath βCC[ 35 ]: C 1 C 7 H 8 bend βCH[ 33 ]:C 7 C 8 H 8 bend 6b[ 34 ]: Ring deform 1[ 12 ]: ring breath

The vibrational levels of phenylacetylene in the S 1 state Symmetry Our result 15 1 b2b b 2 a1a b b2b a16a1 a1a1 409  CC 1 b2b b 1 6a 1 b1b b16b1 b2b2 555  CH 1 b2b2 561  CC a1a a1a a26a2 a1a1 821  CC 1 6a 1 b2b a1a a 1 a1a1 954  CC 2 a1a a19a1 a1a a1a  CC b2b a36a3 a1a b b2b  CC b2b a1a  CC 1 9a 1 a1a a 1 6b 1 b2b  CC 1 9a 1 b2b a1a  CC b2b b 1 b2b a 2 a1a CC 1 a1a1 2013

The vibrational levels of phenylacetylene cation in the D 0 state via transition of selected levels in the S 1 state

Vibrational level Vib symmetry Kwon et al.Lin and TzengDyke et al. S 1 state b 2 10b a 1  CC 1 6a 1 10b 1  CH 1 6b b2b b 2 a1a b a2a a 1 a2a b b2b a16a1 a1a  CC 1 b2b b16b1 b2b a 1 10b 1 a2a  CC 1 a1a a 1 10b 2 a1a a1a a 1 10b b2b a26a2 a1a a 1  CC 1 b2b b 2 a1a a 2 10b 1 b1b a16b16a16b1 b2b a 2 10b 2 a1a b26b2 a1a a 1  CH 1 b2b a a1a a1116a1 a1a  CC 1 b2b  CC 1 10a 1d b1b b1116b1 b2b a36a3 a1a a 2  CC 1 b2b a a1a a 2 6b 1 b2b a 3 10b 1 b1b  CC 1 b2b a1a b b2b a 1 10b b1b a 3 10b 2 a1a a 2 6b 1 10b 1 a1a a2116a2 a1a a1a a1126a1 a1a a1a Summary of vibrational frequencies and their assignment for phenylacetylene in the cation ground state

Angular distribution of electron ionized via different vibration modes Θ e-e- 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 S 1 and D 0 states of the phenylacetylene were determined, as well as the photoelectron angular distribution. Vibronic coupling with 1 A 1 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.