Laboratoire J. A. Dieudonné, UMR 6621 du CNRS, Faculté des Sciences, Parc Valrose, 06108 Nice Cedex 2, France.
J Chem Phys. 2012 May 7;136(17):174309. doi: 10.1063/1.4705278.
In a previous article we have introduced an alternative perturbation scheme to the traditional one starting from the harmonic oscillator, rigid rotator Hamiltonian, to find approximate solutions of the spectral problem for rotation-vibration molecular Hamiltonians. The convergence of our method for the methane vibrational ground state rotational energy levels was quicker than that of the traditional method, as expected, and our predictions were quantitative. In this second article, we study the convergence of the ab initio calculation of effective dipole moments for methane within the same theoretical frame. The first order of perturbation when applied to the electric dipole moment operator of a spherical top gives the expression used in previous spectroscopic studies. Higher orders of perturbation give corrections corresponding to higher centrifugal distortion contributions and are calculated accurately for the first time. Two potential energy surfaces of the literature have been used for solving the anharmonic vibrational problem by means of the vibrational mean field configuration interaction approach. Two corresponding dipole moment surfaces were calculated in this work at a high level of theory. The predicted intensities agree better with recent experimental values than their empirical fit. This suggests that our ab initio dipole moment surface and effective dipole moment operator are both highly accurate.
在之前的一篇文章中，我们介绍了一种从谐振子、刚性转子哈密顿量出发的替代传统微扰方案，以寻找旋转-振动分子哈密顿量谱问题的近似解。我们的方法对甲烷基态振动转动能级的收敛速度比传统方法快，这是预期的，并且我们的预测是定量的。在这第二篇文章中，我们在相同的理论框架内研究了甲烷有效偶极矩的从头计算的收敛性。当应用于球顶的电偶极矩算符的一级微扰给出了先前光谱研究中使用的表达式。更高阶的微扰给出了对应于更高的离心畸变贡献的修正，并首次准确地计算出来。为了通过振动平均场组态相互作用方法求解非谐振动问题，使用了文献中的两个势能面。在这项工作中，我们在一个高水平的理论上计算了两个相应的偶极矩面。预测的强度与最近的实验值比它们的经验拟合更吻合。这表明我们的从头计算偶极矩面和有效偶极矩算符都非常准确。
