Theoretical Study On The Hydrogen Abstraction Reactions CF₃O+CH₄(CD₄)â†'CF₃OH(CF₃OD)+CH₃(CD₃)

The dynamics properties of the hydrogen abstraction reaction CF₃O + CH₄(CD₄) →CF₃OH(CF₃OD) + CH₃(CD₃) is studied by dual-level direct dynamics method. Optimized geometries and frequencies of the stationary points as well as the extra points along the minimum energy path (MEP) are calculated at the B3LYP/6-311G(d, p) level of theory. In order to improve energetics information along the MEP, single-point calculations are carried out at the multi-coefficient correction method based on quadratic configuration interaction with Single and double excitations MC-QCISD//B3LYP level of theory. Furthermore, the rate constants are evaluated by canonical variational transition-state theory with a small-curvature tunneling correction over a wide range of temperature 200-2000 K. The agreement between theoretical and experimental rate constants is good in the measured temperature range. The calculated results show that the variational effect is small and almost neglected over the whole temperature range, whereas, the tunneling correction plays a role in the lower temperature range. The kinetic isotope effect for the reaction is "normal". The values of k_H/k_D are 2.38 at room temperature and they decrease with the temperature increasing. By means of the Gaussian03 program, at the B3LYP/6-311G(d, p) level, the geometries and frequencies of the stationary points (reactant, transition state, and products) are calculated. The minimum energy path (MEP) is...