Dual-level direct dynamics studies for the reactions of dimethyl ether with hydrogen atom and methyl radical

The dual-level direct dynamics approach is employed to study the dynamics of the CH₃OCH₃ + H (R1) and CH₃OCH₃ + CH₃ (R2) reactions. Low-level calculations of the potential energy surface are carried out at the MP2/6-311+G(d,p) level of theory. High-level energetic information is obtained at the QCISD(T) level of theory with the 6-311+G(3df,3pd) basis set. The dynamics calculations are performed using variational transition state theory (VTST) with the interpolated single-point energies (ISPE) method, and small-curvature tunneling (SCT) is included. It is shown that the reaction of CH₃OCH₃ with H (R1) may proceed much easier and with a lower barrier height than the reaction with CH₃ radical (R2). The calculated rate constants and activation energies are in good agreement with the experimental values. The calculated rate constants are fitted to k_R1 = 1.16 × 10^-19 T³ exp(- 1922/T) and k_R2 = 1.66 × 10^-28 T⁵ exp(- 3086/T) cm³ mol^-1 s^-1 over a temperature range 207-2100 K. Furthermore, a small variational effect and large tunneling effect in the lower temperature range are found for the two reactions.