Institute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
J Chem Phys. 2019 Feb 28;150(8):084306. doi: 10.1063/1.5084100.
The vibrational spectra of simple CH -Rg (Rg = He, Ne, Ar, Kr) complexes have been studied by vibrational configuration interaction theory relying on multidimensional potential energy surfaces (PESs) obtained from explicitly correlated coupled cluster calculations, CCSD(T)-F12a. In agreement with experimental results, the series of rare gas atoms leads to rather unsystematic results and indicates huge zero point vibrational energy effects for the helium complex. In order to study these sensitive complexes more consistently, we also introduce configuration averaged vibrational self-consistent field theory, which is a generalization of standard vibrational self-consistent field theory to several configurations. The vibrational spectra of the complexes are compared to that of the methyl cation, for which corrections due to scalar-relativistic effects, high-order coupled-cluster terms, e.g., quadruple excitations, and core-valence correlation have explicitly been accounted for. The occurrence of tunneling splittings for the vibrational ground-state of CH -He has been investigated on the basis of semiclassical instanton theory. These calculations and a direct comparison of the energy profiles along the intrinsic reaction coordinates with that of the hydronium cation, HO, suggest that tunneling effects for vibrationally excited states should be very small.
简单的 CH-Rg（Rg=He、Ne、Ar、Kr）复合物的振动光谱已经通过依赖于从显式相关耦合簇计算（CCSD(T)-F12a）获得的多维势能面（PES）的振动构象相互作用理论进行了研究。与实验结果一致，一系列稀有气体原子导致相当不系统的结果，并表明氦复合物的零点振动能效应非常大。为了更一致地研究这些敏感复合物，我们还引入了构象平均振动自洽场理论，这是对几个构象的标准振动自洽场理论的推广。复合物的振动光谱与甲基阳离子的光谱进行了比较，其中已经明确考虑了标量相对论效应、高阶耦合簇项（例如四重激发）和核价相关的修正。基于半经典瞬时理论，研究了 CH-He 振动基态的隧道分裂。这些计算以及沿着内禀反应坐标的能量分布与水合氢离子（HO）的能量分布的直接比较表明，振动激发态的隧道效应应该很小。
