Exact quantum dynamics and tests of the distorted-wave approximation for the O(³P) + HD reaction

We present accurate quantum-dynamical calculations of isotopic branching probabilities in the O + HD → OH + D or OD + H reaction on a realistic potential-energy surface. The results are used to test several versions of distorted-wave theory in the threshold region. We find that at low energies and low initial rotational quantum numbers, calculations based on distorted waves that are fully coupled within each arrangement are in excellent agreement with accurate quantal reaction probabilities, but deviations occur for higher energies and higher initial rotational quantum numbers. Uncoupled distorted waves or distorted waves with rotational but not vibrational coupling do not lead to accurate reaction probabilities under any conditions, but the relative product vibrational-rotational distributions are quite accurate not only for the fully coupled distorted-wave approximation but also for the rotationally coupled distorted-wave approximation.