A dual-level direct dynamics study on the hydrogen-abstraction reactions of C₂H_n+2Cl_3-n + HBr with n = 1, 2

A dual-level direct dynamics study was carried out for the reactions CH₃CHCl + HBr and CH₃CCl₂ + HBr. The minimum energy path (MEP) for both reactions are obtained by two density functional, BH&H-LYP with basis set 6-311G(d,p) and BB1K with basis set 6-31+G(d,p). The single-point energies along two MEPs are further improved with two methods, G2M and approximate QCISD(T)/6-311++G(3df,2pd), respectively. The similar results are obtained at the two methods. The rate constants for both reactions were evaluated using the improved canonical variational transition-state theory (ICVT) with the small-curvature tunneling correction (SCT) over a wide temperature range of 220-2200 K at the G2M//BH&H-LYP/6-311G(d,p) level. The calculated ICVT/SCT rate constants results are in reasonable agreement with the experimental results and exhibit the negative temperature dependence below 800 K for the reaction CH₃CHCl with HBr. The variational effect and small-curvature tunneling effect are all important in the lower temperature range.