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Photodissociation dynamics of thioanisole on S1, S2 and S3

2008년 8월 12일 15시 03분 04초
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목 <발표Ⅱ>
저자 및
임정식, 윤준호1, 김상규
한국과학기술원 화학과, Korea
1한국과학기술원 화학, Korea
The S-CH3 dissociation dynamics of thioanisole (C6H5SCH3) along the S-CH2 dissociation coordinate on S1, S2 and S3 was elucidated by using velocity map ion imaging. The kinetic energy release and anisotropy parameter corresponding to each states as series of pump energy could resolve unique characters of each states by the aid of electronic structure calculation. Moreover, adiabatic excitation energy and bond dissociation energy are also determined experimentally. In a separate experiment, REMPI spectrum of first excited state and PHOFEX of CH3 radical was obtained for giving deep insight to the photochemistry of thioanisole. For the detail, A (1ππ*, S1), C (1ππ*, S3) and B (1nσ*, S2) states are indentified as bound and strongly repulsive potential along the S-CH3 distance coordinate, respectively. Fundamentally, 1-dim potential energy curves are quite similar compared to thiophenol (C6H5SH) except relative potential energy. But, detailed photodissociation dynamics is different in multi dimensional view. As an analog of thiophenol, methyl moiety causes the modulation of potential energy surfaces including relative location and topography of each states because different electronic environment and increased internal degrees of freedom. Especially, CCSC torsion potential is significantly differentiated. As a visible result, these differences enhance internal energy excitation and the yield of A state of fragmented radical in the kinetic energy release spectrum. It seems to be conjectured that the nucleus wavepacket bifurcated at S0/S2 conical intersection is following adiabatic pathway due to the enhanced torsion motion on the 2-dim potential energy surfaces. And also it is found that the wavepacket prepared on different Franck-Condon region on S-C stretching coordinate of repulsive S2 could induce different yield of each states.