Methyl substitution effects on the non-adiabatic dynamics of benzene: lifting three-state quasi-degeneracy at conical intersections
Methyl substitution effects on the non-adiabatic dynamics of benzene: lifting three-state quasi-degeneracy at conical intersections
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DOI：
10.1039/c9cp06164a
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发表时间：
2020-02-07
影响因子：
3.3
通讯作者：
Suzuki, Toshinori
中科院分区：
文献类型：
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作者：
Adachi, Shunsuke;Suzuki, Toshinori
此前，对S-2态苯非绝热动力学的理论计算表明，S-2/S-1和S-1/S-0圆锥形交叉点（CI）促进弹道核波包从S-2运动到S-0（快通道）并分支到S-1（慢通道）。在本文中，我们提出了用真空紫外激光测量的苯及其甲基衍生物（甲苯和邻二甲苯）的时间分辨光电子能谱，清楚地揭示了快通道和慢通道。苯的两个CI之间的波包传播时间极短，表明两者彼此非常接近，而甲基取代延长了传播时间并降低了进入快速通道的支化比。结果表明，苯中三种态的准简并性是通过甲基取代引起的 CI 的几何位移而提升的。
Previously, theoretical calculations on the non-adiabatic dynamics of benzene from the S-2 state have indicated that the S-2/S-1 and S-1/S-0 conical intersections (CIs) facilitate ballistic nuclear wavepacket motion from S-2 to S-0 (fast channel) and branching to S-1 (slow channel). In this paper, we present time-resolved photoelectron spectra of benzene and its methyl-derivatives (toluene and o-xylene) measured with a vacuum-UV laser, which clearly reveal both the fast and slow channels. The extremely short propagation time of the wavepacket between the two CIs of benzene indicates that the two are in close proximity to each other, while methyl substitution extends the propagation time and decreases the branching ratio into the fast channel. The results suggest that the quasi-degeneracy of the three states in benzene is lifted by the geometrical shifts of the CIs by methyl substitution.