Full-dimensional time-dependent treatment for diatom–diatom reactions: The H2+OH reaction

Extending our previous studies for the H2+OH reaction in five mathematical dimensions (5D) J. Chem. Phys. 99, 5615 (1993); 100, 2697 (1994), we present in this paper a full-dimensional (6D) dynamics study for the title reaction. The 6D treatment uses the time-dependent wave-packet approach and employs discrete variable representations for three radial coordinates and coupled angular momentum basis functions for three angular coordinates. The present 6D study employs an energy projection method to extract reaction probabilities for a whole range of energies from a single wave-packet propagation, while previous studies produced only energy-averaged reaction probability from a single wave-packet propagation. The application of the energy-projection method allows us to efficiently map out the energy dependence of the reaction probability on a fine grid which revealed surprisingly sharp resonancelike features at low collision energies on the Schatz–Elgersma potential surface. Our calculation shows that the potential-averaged 5D treatment can produce reaction probabilities essentially indistinguishable from the full-dimensional result. We also report initial state-selected reaction cross sections and rate constants which are in good agreement with our previous calculations. The effect of OH vibration on H2+OH reaction is examined in the present study and our calculation shows that the OH vibration can enhance the rate constant by about a factor of 1.7 in good agreement with the experimental estimate of about 1.5.