A reduced dimensionality quantum mechanical study of the H + HCF3 ↔ H2 + CF3 reaction.

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 ↔ H2 + 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 H2 with D2. These results also clearly demonstrate the significance of quantum tunnelling in the reaction