Ab initio direct dynamics studies on the reactions of H atoms with CCl₄ and CHCl₃

By means of ab initio direct dynamics method, the reactions H + CCl₄ → CCl₃ + HCl (1) and H + CHCl₃ → products (2) have been investigated theoretically to reveal their dynamical properties. The minimum energy paths (MEPs) of both reactions are calculated at the BH&H-LYP/6-311G(d,p) level, and the energies along the MEPs are further refined at the PMP4/6-311 + G(3df,2p) (single-point) level. For reaction 2, both reaction channels, H-abstraction and Cl-abstraction, have been identified. Thus, the rate constants for each reaction channel as well as reaction 1 are calculated by the canonical variational transition state theory incorporating the small-curvature tunneling correction in the temperature range 200-5000 K. For reaction 1, the theoretical rate constants are in good agreement with the experimental values over the measured temperature range. For reaction 2, the total rate constants, which are calculated from the sum of the individual rate constants, are in excellent agreement with the experimental ones, and the temperature dependence of the branching ratios indicate that, at low-temperature range (T < 667 K), H-abstraction is the major channels, whereas Cl-abstraction channels will significantly contribute to the whole reaction rate as the temperature increases.