Helicity decoupled quantum dynamics and capture model cross sections and rate constants for O(¹D) + H₂ → OH + H

We study, within a helicity decoupled quantum approximation, the total angular momentum J dependence of reaction probabilities for the reaction O(¹D) + H₂ → OH + H. A recently developed real wave packet approach is employed for the quantum calculations. The ab initio based, ground electronic (X̄ ¹A') potential energy surface of Ho et al. (T-S. Ho, T. Hollebeeck, H. Rabitz, L. B. Harding and G. C. Schatz, J. Chem. Phys., 1996, 105, 10472) is assumed for most of our calculations, although some calculations are also performed with a recent surface due to Dobbyn and Knowles. We find that the low J reaction probabilities tend to be, on average, slightly lower than the high J probabilities. This effect is also found to be reproduced in classical trajectory calculations. A new capture model is proposed that incorporates the available quantum data within an orbital angular momentum or l-shifting approximation to predict total cross sections and rate constants. The results agree well with classical trajectory results and the experimental rate constant at room temperature. However, electronically non-adiabatic effects may become important at higher temperature.