Kleiner Isabelle, Hougen Jon T
Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR 7583 CNRS/IPSL, Universités Paris Est & Paris Diderot , 61 avenue du Général de Gaulle, F-94010 Créteil cedex, France.
Sensor Science Division, NIST , Gaithersburg, Maryland 20899-8441, United States.
J Phys Chem A. 2015 Oct 29;119(43):10664-76. doi: 10.1021/acs.jpca.5b08437. Epub 2015 Oct 15.
A new hybrid-model fitting program for methylamine-like molecules has been developed, on the basis of an effective Hamiltonian in which the ammonia-like inversion motion is treated using a tunneling formalism, whereas the internal-rotation motion is treated using an explicit kinetic energy operator and potential energy function. The Hamiltonian in the computer program is set up as a 2 × 2 partitioned matrix, where each diagonal block contains a traditional torsion-rotation Hamiltonian (as in the earlier program BELGI), and the two off-diagonal blocks contain tunneling terms. This hybrid formulation permits the use of the permutation-inversion group G6 (isomorphic to C(3v)) for terms in the two diagonal blocks but requires G12 for terms in the off-diagonal blocks. The first application of the new program is to 2-methylmalonaldehyde. Microwave data for this molecule were previously fit using an all-tunneling Hamiltonian formalism to treat both large-amplitude motions. For 2-methylmalonaldehyde, the hybrid program achieves the same quality of fit as was obtained with the all-tunneling program, but fits with the hybrid program eliminate a large discrepancy between internal rotation barriers in the OH and OD isotopologs of 2-methylmalonaldehyde that arose in fits with the all-tunneling program. This large isotopic shift in internal rotation barrier is thus almost certainly an artifact of the all-tunneling model. Other molecules for application of the hybrid program are mentioned.
基于一种有效哈密顿量，已开发出一种用于甲胺类分子的新型混合模型拟合程序。在该哈密顿量中，氨类反转运动采用隧穿形式进行处理，而内旋转运动则使用显式动能算符和势能函数进行处理。计算机程序中的哈密顿量被设置为一个2×2分块矩阵，其中每个对角块包含一个传统的扭转 - 旋转哈密顿量（如早期程序BELGI中的那样），两个非对角块包含隧穿项。这种混合公式允许对两个对角块中的项使用置换反转群G6（同构于C(3v)），但非对角块中的项需要G12。新程序的首次应用是针对2 - 甲基丙二醛。该分子的微波数据先前使用全隧穿哈密顿量形式来处理这两种大振幅运动。对于2 - 甲基丙二醛，混合程序实现了与全隧穿程序相同的拟合质量，但使用混合程序进行的拟合消除了在全隧穿程序拟合中出现的2 - 甲基丙二醛的OH和OD同位素体在内旋转势垒方面的巨大差异。因此，内旋转势垒中这种大的同位素位移几乎肯定是全隧穿模型的一个人为因素。文中还提到了混合程序的其他应用分子。
