W e present accurate quantum-dynamical calculations of isotopic branching probabilities in t h e 0 + 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 t h e threshold region. W e 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 quanta1 reaction

more »

... es, 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 distortedwave approximation but also for t h e rotationally coupled distorted-wave approximation.