A reduced dimensionality quantum mechanical study of the H + HCF3 <-> H-2 + CF3 reaction

作者：Shan Xiao^*; Clary David C

来源：Physical Chemistry Chemical Physics, 2013, 15(42): 18530-18538.

DOI：10.1039/c3cp52170b

Recently, the authors developed a new method to construct a two-dimensional potential energy surface (PES) for use in reduced-dimensionality quantum scattering calculations in chemical reactions. In this approach the minimum energy path of a reaction was utilized and the rest of the surface was fitted by a Morse function. Here we test this method on the H + HCF3 <-> H-2 + CF3 reaction. The geometry optimizations and frequency calculations are done at the MP2/cc-pVTZ level of theory, while the energies are calculated at the CCSD(T)/aug-cc-pVTZ level. An adiabatic energy barrier of 59.61 kJ mol(-1) for the forward direction is suggested by our calculations, and the reaction is endothermic by 10.55 kJ mol(-1) in the same direction. When compared to classical transition state theory, quantum scattering calculations suggest that a tunnelling effect can be observed in both forward and backward reactions. For the forward direction, the quantum tunnelling is important at temperatures typically lower than 300 K. It has a greater contribution to the backward reaction, and is over a wider temperature range from 200 K to 1000 K. We also conducted an analysis of the kinetic isotope effects on the backward reaction by replacing H-2 with D-2. These results also clearly demonstrate the significance of quantum tunnelling in the reaction.

• 出版日期2013