Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455-0431, USA.
J Chem Phys. 2017 Jul 28;147(4):044311. doi: 10.1063/1.4994923.
The photodissociation of thioanisole is very interesting because the experiments of Lim and Kim provide evidence for mode-specific effects on the product distribution. They showed that, with a specific S-CH stretching mode being excited as the reagent is excited to the S electronic state, there is a sharp increase in the proportion of the ground-state product to the excited-state product. In the present work, we report 78 011 full-dimensional semiclassical multi-state trajectories of the photodissociation process using the coherent switching with decay of mixing dynamics method. The potential surfaces and couplings are based on electronic structure calculations that include dynamic correlation through second order perturbation theory. We report results for four sets of initial conditions, one corresponding roughly to 0-0 excitation and three corresponding to exciting one vibrational mode, to look for mode-specific effects. The simulations show no significant mode-specific effect on the product energy distributions, but they do show an effect on the distribution of minimum-energy gaps in the trajectories and on the lifetime for dissociation. In particular, excitation of the S-CH stretching mode leads to trajectories passing closer to the S-S conical intersection and to shorter lifetimes. This provides a possible explanation of why experimental results are different for excitation of this vibration.
硫醚的光解非常有趣，因为 Lim 和 Kim 的实验为产物分布的模式特异性效应提供了证据。他们表明，当试剂被激发到 S 电子态时，特定的 S-CH 伸缩模式被激发，基态产物与激发态产物的比例会急剧增加。在本工作中，我们使用相干切换与混合动力学方法的衰减，报告了 78011 个全维半经典多态光解过程的轨迹。势能面和耦合基于包括通过二级微扰理论的动态相关的电子结构计算。我们报告了四组初始条件的结果，一组大致对应于 0-0 激发，三组对应于激发一个振动模式，以寻找模式特异性效应。模拟结果表明，产物能量分布没有明显的模式特异性效应，但在轨迹中的最小能量间隙分布和离解寿命上确实存在效应。特别是，S-CH 伸缩模式的激发导致轨迹更接近 S-S 锥形交叉，并且离解寿命更短。这为为什么实验结果对这种振动的激发不同提供了一种可能的解释。
