Kowalewski M, Mikosch J, Wester R, de Vivie-Riedle R
Department of Chemistry, Ludwig-Maximilians-Universität , D-81377 Munich, Germany.
J Phys Chem A. 2014 Jul 3;118(26):4661-9. doi: 10.1021/jp503974u. Epub 2014 Jun 19.
The reactive collision of chloride anions and methyl iodide molecules forming iodide anions and methyl chloride is a typical example of a concerted bimolecular nucleophilic substitution (SN2) reaction. We present wave packet dynamics calculations to investigate quantum effects in the collinear gas phase reaction. A new type of reduced coordinate system is introduced to allow for an efficient solution of the time-dependent Schrödinger equation on an ab initio potential energy surface. The reduced coordinates were designed to study the direct rebound mechanism under the Walden inversion. Especially the suppressed direct rebound mechanism at low collision energies, the quantum effects of the initial state preparation and the influence of the CH3 inversion mode are addressed. The internal energy distributions of the molecular product are evaluated from the wave packet calculations and compared to experimental results obtained with crossed-beam velocity map ion imaging. The observed reactivity is discussed in light of a dynamical barrier, a concept that is illustrated by the wave packet dynamics.
氯离子与碘甲烷分子发生反应性碰撞形成碘离子和氯甲烷，这是协同双分子亲核取代（SN2）反应的一个典型例子。我们进行了波包动力学计算，以研究共线气相反应中的量子效应。引入了一种新型的约化坐标系，以便在从头算势能面上高效求解含时薛定谔方程。设计约化坐标是为了研究瓦尔登反转下的直接反弹机制。特别讨论了低碰撞能量下被抑制的直接反弹机制、初始态制备的量子效应以及CH3反转模式的影响。从波包计算中评估分子产物的内能分布，并与通过交叉束速度映射离子成像获得的实验结果进行比较。根据动力学势垒对观察到的反应性进行了讨论，波包动力学阐明了这一概念。
