Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4, Kosygina Str., Moscow 119991, Russia.
J Phys Chem B. 2010 Dec 30;114(51):17102-12. doi: 10.1021/jp1073472. Epub 2010 Dec 8.
Intramolecular tunneling of a hydrogen atom in formic acid at low temperatures has been studied theoretically on the basis of quantum-chemical modeling of HCOOH@Nb(12) clusters. Three noble matrixes (Ar, Kr, and Xe) are considered. Energetic and geometric parameters as well as vibrational frequencies for the formic acid in cis and trans configurations surrounded by 12 Nb atoms are calculated within the frame of the MP2 approach with extended basis sets. The rate constant of HCOOH cis-trans conversion is analyzed by taking into account matrix reorganization and the change of HCOOH position in the cluster. The matrix reorganization is considered within the Debye model of lattice vibrations, whereas the external motion of HCOOH in the cluster is treated using the Einstein model of solids. It has been shown that the literature experimental data on the cis to trans tunneling reaction in the formic acid can be accounted for within the proposed mechanism, which describes the matrix reorganization and the change of the HCOOH position in the noble gas matrix, with fitting parameters of the suggested theoretical model attaining reasonable values.
在基于 HCOOH@Nb(12) 团簇的量子化学建模的基础上，从理论上研究了低温下甲酸分子内氢原子的分子内隧道效应。考虑了三种贵金属基质（Ar、Kr 和 Xe）。在扩展基组的 MP2 方法框架内，计算了由 12 个 Nb 原子包围的顺式和反式构型甲酸的能量和几何参数以及振动频率。考虑到基质重排和 HCOOH 在团簇中位置的变化，分析了 HCOOH 顺反转化的速率常数。基质重排是在晶格振动的德拜模型中考虑的，而 HCOOH 在团簇中的外部运动是使用固体的爱因斯坦模型来处理的。结果表明，在所提出的机制中可以解释甲酸中顺式到反式隧道反应的文献实验数据，该机制描述了贵金属基质中基质重排和 HCOOH 位置的变化，所提出的理论模型的拟合参数达到了合理的值。
