Quantum dynamics of the O(P-3)+CH4 -> OH+CH3 reaction: An application of the rotating bond umbrella model and spectral transform subspace iteration

We have applied the rotating bond umbrella (RBU) model to perform time-independent quantum scattering calculations of the O(P-3)+CH4--> OH+CH3 reaction based on a realistic analytic potential energy surface. The calculations are carried out in hypercylindrical coordinates with a log-derivative method incorporating a guided spectral transform (GST) subspace iteration technique. A single sector hyperspherical projection method is used for applying the boundary conditions. The results show that ground-state CH4 gives CH3 that is rotationally cold. For CH4 initially vibrationally excited in the C-H stretch or the H-CH3 bending mode, a bimodal CH3 rotational distribution has been observed. The product OH is a little vibrationally excited, while the umbrella mode of CH3 is moderately excited. Vibrational excitation enhances the reactivity substantially. The calculated rate constants are in good agreement with experimental measurements. (C) 2000 American Institute of Physics. [S0021-9606(00)01301-5].