Helicity decoupled quantum dynamics and capture model cross sections and rate constants for O(D-1)+H-2 -> OH+H

We study, within a helicity decoupled quantum approximation, the total angu lar momentum J dependence of reaction probabilities for the reaction O(D-1) + H-2 --> OH + H. A recently developed real wave packet approach is employ ed for the quantum calculations. The ab initio based, ground electronic (X) over tilde (1)A') potential energy surface of Ho et al. (T-S. Ho, T. Holle beeck, H. Rabitz, L. B. Harding and G. C. Schatz, J. Chem. Phys., 1996, 105 , 10472) is assumed for most of our calculations, although some calculation s are also performed with a recent surface due to Dobbyn and Knowles. We fi nd that the low J reaction probabilities tend to be, on average, slightly l ower than the high J probabilities. This effect is also found to be reprodu ced in classical trajectory calculations. A new capture model is proposed t hat incorporates the available quantum data within an orbital angular momen tum or l-shifting approximation to predict total cross sections and rate co nstants. The results agree well with classical trajectory results and the e xperimental rate constant at room temperature. However, electronically non- adiabatic effects may become important at higher temperature.