Reduced dimensionality calculations of quantum reactive scattering for the H+CH4→H2+CH3 reaction

The dynamics for the H+CH4→H2+CH3 reaction has been studied using reduced dimensionality quantum-mechanical theory. The system is treated as a linear four-atom chemical reaction, reducing the system to a three-dimensional scattering problem. The vibrational modes of ν1 and ν4 of CH4, the stretching vibration of H2, and the umbrella ν2 mode of CH3 are taken into consideration in the reaction dynamics based on the vibrational analysis along the reaction path. The semiempirical potential energy surface which has recently been developed by Jordan and Gilbert J. Chem. Phys. 102, 5669 (1995) is employed. Rotationally averaged cross sections and thermal rate constants are calculated using an energy-shifting approximation in order to take into account the effect of all the degrees of freedom. It is shown that excitation of the ν1 mode of CH4 significantly enhances the reactivity, indicating that there is a strong coupling between the ν1 mode of CH4 and the reaction coordinate. The vibrational state distributions for the products H2 and CH3 have also been studied. In the energy range considered here, the population of vibrationally excited H2 is found to be very small, while the umbrella ν2 mode of CH3 is found to be excited.