Reaction-path dynamics and theoretical rate constants for the CH3F+Cl->HCl+CH2F reaction by direct dynamics method

Ab initio calculations were carried out for the hydrogen abstraction reaction from fluoromethane by chlorine atom. Optimized geometries and frequencies were computed at the MP2/6-31+G(d) level of theory for reactants, products, and transition state, as well as 15 points along the minimum energy path(MEP). Energies were obtained by a single-point calculation at the QCISD(T)/6-311G(d,p) and MP2/6-311+G(3df,2p) levels of theory to produce the potential energy information at the G2(MP2) level of theory. The vibrational adiabatic potential curve was found to have two barriers due to large variational effects in this system. The rate constants were calculated for the temperature range 200-700 K by using variational transition state theory (VTST) with simple tunneling corrections. While a general agreement was found with experimental values when using improved canonical VTST for most of the temperature range, the calculated Arrhenius slope was too steep in comparison to experiment for lower temperatures.