Department of Physics and Materials Engineering, Hefei Normal University, Hefei 230061, China.
Department of Chemistry, Stanford University, Stanford, California 94305, United States.
J Phys Chem B. 2021 Apr 1;125(12):3163-3177. doi: 10.1021/acs.jpcb.0c11148. Epub 2021 Mar 17.
We present an experimentally parametrized molecular dynamics study of single-molecule and collective orientational relaxation in neat benzonitrile through the analysis of the reorientational anisotropy and polarizability anisotropy time correlation function (PA-TCF). The simulations show that the PA-TCF is dominated by collective reorientation after 20 ps. Collective reorientation is found to be slower than single-molecule reorientation by a factor of 1.67, consistent with recent experiments. The simulations provide direct evidence of local antiparallel benzonitrile configurations. These structures, which have been the center of some debate, are responsible for the slower rate of collective versus single-molecule reorientation in the liquid. Further structural analysis indicates that significant Coulombic interactions between the nitrile group and hydrogen atoms on adjacent molecules play a role in the formation of the antiparallel structures. The single-molecule dynamics reflected in the anisotropy are complex and consist of a ballistic regime, restricted angular diffusion, and spatially anisotropic free diffusion. The principal components of the rotational diffusion tensor are independently obtained and shown to reproduce the free diffusion regime of the anisotropy for each principal axis according to the predictions of a previous theory.
我们通过分析重取向各向异性和极化率各向异性时间相关函数 (PA-TCF)，对纯净苯腈中单分子和集体取向弛豫进行了实验参数化分子动力学研究。模拟表明，PA-TCF 在 20 ps 后主要由集体重取向控制。集体重取向比单分子重取向慢 1.67 倍，与最近的实验结果一致。模拟提供了局部反平行苯腈构型的直接证据。这些结构一直是一些争论的焦点，它们导致液体中集体与单分子重取向的速率较慢。进一步的结构分析表明，腈基和相邻分子上氢原子之间的显著库仑相互作用在反平行结构的形成中起作用。各向异性中反映的单分子动力学很复杂，包括弹道阶段、受限角扩散和各向异性自由扩散。旋转扩散张量的主成分被独立获得，并根据先前理论的预测，表明它们各自的主轴根据各向异性的自由扩散阶段进行复制。
