Nandipati K R, Vasilyev O A, Navarkin I S, Solomonik V G, Domcke W
Department of Chemistry, Technical University of Munich, D-85747 Garching, Germany.
Department of Physics, Ivanovo State University of Chemistry and Technology, 153000 Ivanovo, Russia.
J Chem Phys. 2020 Mar 7;152(9):094304. doi: 10.1063/1.5131739.
Transition metal tetrahalides are a class of highly symmetric molecules for which very few spectroscopic data exist. Exploratory ab initio calculations of electronic potential energy functions indicate that the equilibrium molecular geometries of the vanadium, niobium, and tantalum tetrafluorides (i.e., VF, NbF, and TaF) exhibit strong distortions from the tetrahedral configuration in their electronic ground state (E) and first excited state (T) along the nuclear displacement coordinates of e symmetry. The distortions result from the E × e and T × e Jahn-Teller (JT) effects, respectively. In addition, there are weaker distortions in the T state along the coordinates of t symmetry due to the T × t JT effect. The description of the large-amplitude dynamics induced by these JT effects requires the construction of JT Hamiltonians beyond the standard model of JT theory, which is based on Taylor expansions up to second order in normal-mode displacements. These higher-order JT Hamiltonians were constructed in this work by expansions of the electronic potentials of the title molecule in terms of symmetry invariant polynomials in symmetry-adapted nuclear displacement coordinates for the bending modes of VF. A multi-configuration electronic structure method was employed to determine the coefficients of these high-order polynomial expansions from first principles. Using these large-amplitude Jahn-Teller Hamiltonians, the vibronic spectra of VF were computed. The spectra illustrate the effects of large-amplitude fluxional nonadiabatic dynamics due to exceptionally strong E × e and T × e JT couplings. In addition, the vibronic spectrum of the T × (e + t) JT effect, including the bending mode of t symmetry, was computed. The spectrum displays strong inter-mode coupling effects exhibiting a vibronic structure, which is substantially different from that predicted by independent-mode approximation. These results represent the first ab initio study of dynamical Jahn-Teller effects in VF.
过渡金属四卤化物是一类高度对称的分子，目前关于它们的光谱数据非常少。对电子势能函数进行的探索性从头算计算表明，钒、铌和钽的四氟化物（即VF、NbF和TaF）在其电子基态（E）和第一激发态（T）下，沿着e对称性的核位移坐标，其平衡分子几何结构呈现出与四面体构型的强烈畸变。这些畸变分别是由E×e和T×e Jahn-Teller（JT）效应引起的。此外，由于T×t JT效应，T态沿着t对称性坐标存在较弱的畸变。要描述由这些JT效应引起的大幅度动力学，需要构建超越JT理论标准模型的JT哈密顿量，该标准模型基于在简正模式位移中展开到二阶的泰勒展开式。在这项工作中，通过根据VF弯曲模式的对称适配核位移坐标中的对称不变多项式展开标题分子的电子势能，构建了这些高阶JT哈密顿量。采用多组态电子结构方法从第一性原理确定这些高阶多项式展开的系数。利用这些大幅度Jahn-Teller哈密顿量，计算了VF的振转光谱。这些光谱说明了由于异常强的E×e和T×e JT耦合导致的大幅度通量非绝热动力学的影响。此外，还计算了包括t对称性弯曲模式在内的T×(e + t) JT效应的振转光谱。该光谱显示出强烈的模间耦合效应，呈现出一种振转结构，与独立模式近似预测的结构有很大不同。这些结果代表了对VF中动力学Jahn-Teller效应的首次从头算研究。
