Product multiplet branching in the $O(1D)+H2→OH(2Π)+H$ reaction

The statistical model of atom-diatom insertion reactions is combined with coupled-states capture theory and used to calculate product multiplet-resolved integral cross sections for the title reaction. This involves an ab initio determination of the four electronic potential energy surfaces that correlate with the products $(1,3A′$ and $A″1,3),$ and an accurate description of the electronic and spin-orbit couplings between them. The dependence of the resulting cross sections on the final-state rotational quantum number shows a statistical behavior similar to that observed in earlier studies of the reaction in which only the lowest $(1A′)$ potential was retained. In addition, however, the present calculations provide information on the branching between the $OH(2Π)$ multiplet levels. Although the two spin-orbit manifolds are predicted to be equally populated, we find a strong propensity for the formation of the $Π(A′)$ Λ-doublet states. These two predictions confirm the experimental results of Butler, Wiesenfeld, Gericke, Brouard, and their co-workers. The nonstatistical population of the OH Λ-doublet levels is a consequence of the bond breaking in the intermediate $H2O$ complex and is preserved through the multiple curve crossings as the products separate. This exit-channel coupling is correctly described by the present theory.