Dual level direct ab initio and density-functional theory dynamics study on the unimolecular decomposition of CH₃OCH₂ radical

We presented a direct ab initio and density-functional theory dynamics study of the thermal rate constants of the unimolecular decomposition reaction of CH₃OCH₂ → CH₂O + CH₃ at a wide temperature range of 200-2500 K. MPW1K/6-31+G(d,p), MP2/6-31+G(d,p), and QCISD/6-31+G(d,p) methods were employed to optimize the geometries of all stationary points and to calculate the minimum energy path (MEP). The energies of all the stationary points were refined at the QCISD(T)/aug-cc-pVTZ level of theory. The rate constants were evaluated based on the energetics from the QCISD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) level of theory using both microcanonical variational transition state theory (μVT) and canonical variational transition state theory (CVT) in the temperature range of 200-2500 K. The calculated rate constants at the QCISD-(T)/ aug-cc-pVTZ//MPW1K/6-31+G(d,p) level of theory are in good agreement with experimental data. The fitted three-parameter Arrhenius expression from the μVT rate constants in the temperature range 200-2500 K is κ = 4.45 × 10¹⁴T^-0.22 e^{(-1.37×10 4/T)} s^-1.