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Nonadiabatic Dynamics of Photoexcited cis-Stilbene Using Ab Initio Multiple Spawning.
The Journal of Physical Chemistry B ( IF 3.3 ) Pub Date : 2020-05-19 , DOI: 10.1021/acs.jpcb.0c03344
Hayley Weir 1, 2 , Monika Williams 1, 2 , Robert M Parrish 1, 2 , Edward G Hohenstein 1, 2 , Todd J Martínez 1, 2
Affiliation  

The photochemistry of cis-stilbene proceeds through two pathways: cis-trans isomerization and ring closure to 4a,4b-dihydrophenanthrene (DHP). Despite serving for many decades as a model system for photoisomerization, the photodynamics of cis-stilbene is still not fully understood. We use ab initio multiple spawning on a SA-2-CASSCF(2,2) potential energy surface to simulate the nonadiabatic dynamics of isolated cis-stilbene. We find the cyclization (to DHP and cis-stilbene) and isomerization (to trans- and cis-stilbene) reaction coordinates to be orthogonal; branching between the two pathways is determined on the S1 excited state within 150 fs of photoexcitation. Trajectory basis functions (TBFs) undergoing cyclization decay rapidly to the ground state in 250 fs, while TBFs moving along the isomerization coordinate remain on the excited state longer, with the majority decaying between 300 and 500 fs. We observe three avoided crossing regions in the dynamics: two along the isomerization coordinate (displaying pyramidalization and migration of an ethylenic hydrogen or phenyl group), and one DHP-like conical intersection along the cyclization coordinate. The isomeric form of the vibrationally hot photoproducts (as determined by measurement 2 ps after photoexcitation) is determined within less than 50 fs of decay to the ground state mediated by passage through a conical intersection. Excess vibrational energy of ground state cis- and trans-stilbene is channelled into phenyl torsions (with mostly opposing directionality). Our simulations are validated by direct comparison to experiment for the absorption spectrum, branching ratio of the three photoproducts (44:52:4 cis-stilbene:trans-stilbene:DHP), and excited state lifetime (520 ± 40 fs).

中文翻译:

从头算起多重产生的光激发顺式-Stilbene的非绝热动力学。

顺式-苯乙烯的光化学通过两个途径进行:顺式-反式异构化和闭环成4a,4b-二氢菲(DHP)。尽管作为光异构化的模型系统已有数十年的历史,但顺式-二苯乙烯的光动力学仍然没有被完全理解。我们使用从头开始在SA-2-CASSCF(2,2)势能表面上多次重生来模拟孤立的顺式-sti的非绝热动力学。我们发现环化(以DHP和-二苯乙烯)和异构化(以反式-与-二苯乙烯)反应的坐标是正交的; 在S 1上确定两个路径之间的分支光激发150 fs内的激发态。经历环化作用的轨迹基函数(TBF)在250 fs内迅速衰减至基态,而沿异构化坐标移动的TBFs在激发态上停留的时间更长,大部分衰减在300至500 fs之间。我们在动力学中观察到三个避免的交叉区域:两个沿着异构化坐标(显示乙烯氢或苯基的锥体化和迁移),以及一个沿着环化坐标的类似DHP的圆锥形交叉点。振动热的光产物的同分异构形式(由光激发后2 ps的测量确定)是在不到50 fs的衰减范围内确定的,该衰减是通过圆锥形交叉点介导的。基态顺式的多余振动能-和反式-二苯乙烯被引入苯基扭转(方向性大多相反)。我们的仿真通过与吸收光谱,三种光产物的支化比(44:52:4顺式-::反式-sti:DHP)和激发态寿命(520±40 fs)的直接比较进行了验证。
更新日期:2020-07-02
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