Leontyev I V, Tachiya M
National Institute of Advanced Industrial Science and Technology, AIST Central 5, Tsukuba, Ibaraki 305-8565, Japan.
J Chem Phys. 2005 Dec 8;123(22):224502. doi: 10.1063/1.2131054.
The intermolecular electron transfer in a solute pair consisting of pyrene and dimethylaniline is investigated in a nonpolar solvent, n-hexane. The earlier elaborated approach [M. Tachiya, J. Phys Chem. 97, 5911 (1993)] is used; this method provides a physically relevant background for separating inertial and inertialess polarization responses for both nonpolarizable and polarizable molecular level simulations. The molecular-dynamics technique was implemented for obtaining the equilibrium ensemble of solvent configurations. The nonpolar solvent, n-hexane, was treated in terms of OPLS-AA parametrization. Solute Lennard-Jones parameters were taken from the same parametrization. Solute charge distributions of the initial and final states were determined using ab initio level [HF/6-31G(d,p)] quantum-chemical calculations. Configuration analysis was performed explicitly taking into account the anisotropic polarizability of n-hexane. It is shown that the Gaussian law well describes calculated distribution functions of the solvent coordinate, therefore, the rate constant of the ET reaction can be characterized by the reorganization energy. Evaluated values of the reorganization energies are in a range of 0.03-0.11 eV and significant contribution (more then 40% of magnitude) comes from anisotropic polarizability. Investigation of the reorganization energy lambda dependence on the solute pair separation distance d revealed unexpected behavior. The dependence has a very sharp peak at the distance d=7 A where solvent molecules are able to penetrate into the intermediate space between the solute pair. The reason for such behavior is clarified. This new effect has a purely molecular origin and cannot be described within conventional continuum solvent models.
在非极性溶剂正己烷中研究了由芘和二甲基苯胺组成的溶质对中的分子间电子转移。采用了早期详细阐述的方法[M. 立谷，《物理化学杂志》97, 5911 (1993)]；该方法为非极化和极化分子水平模拟中分离惯性和非惯性极化响应提供了物理相关背景。采用分子动力学技术获得溶剂构型的平衡系综。非极性溶剂正己烷按照OPLS - AA参数化进行处理。溶质的 Lennard - Jones 参数取自相同的参数化。初始态和终态的溶质电荷分布使用从头算水平[HF/6 - 31G(d,p)]量子化学计算确定。在明确考虑正己烷各向异性极化率的情况下进行构型分析。结果表明，高斯定律能很好地描述计算得到的溶剂坐标分布函数，因此，电子转移反应的速率常数可以用重组能来表征。重组能的评估值在0.03 - 0.11 eV范围内，且各向异性极化率贡献显著（超过幅值的40%）。对重组能λ随溶质对分离距离d的依赖性研究揭示了意想不到的行为。在距离d = 7 Å处，该依赖性有一个非常尖锐的峰值，此时溶剂分子能够渗透到溶质对之间的中间空间。这种行为的原因得到了阐明。这种新效应具有纯粹的分子起源，无法用传统的连续介质溶剂模型来描述。
