Dual-Level Direct Dynamics Calculations of the Reaction Rates for a Jahn−Teller Reaction:  Hydrogen Abstraction from CH₄or CD₄by O(³P)

We report calculations of the reaction rates of O(3P) + CH4 → OH + CH3 and O(3P) + CD4 → OD + CD3 over the temperature range 300−2500 K. The calculations are based on variational transition state theory in curvilinear coordinates with transmission coefficients calculated by the microcanonical optimized multidimensional tunneling approximation. A dual-level algorithm is used for the dynamical calculations. The higher level is UMP2/cc-pVTZ, and two lower levels are employed: PM3-SRP and an analytical potential energy surface. Using the canonical unified statistical model with microcanonical optimized multidimensional tunneling contributions, we obtain good agreement with experimental rate constants.