We report exact J = 0 quantum reaction probability for the title reaction using a wave packet method. It is shown that the reaction is almost completely dominated by the capture of the reactants, because of its large exothermicity and barrierless nature. As a result, the integral cross section can be accurately determined by capture probabilities. The calculated quantum rate constant is in good agreement with the earlier quasi-classical trajectory results except at low temperatures. The discrepancy is discussed. (C) 2008 Elsevier B.V. All rights reserved.