Quantum dynamics of the O + OH --> H + O2 reaction at low temperatures.

We report quantum dynamics calculations of the O + OH --> H + O(2) reaction on two different representations of the electronic ground state potential energy surface (PES) using a time-independent quantum formalism based on hyperspherical coordinates. Calculations show that several excited vibrational levels of the product O(2) molecule are populated in the reaction. Rate coefficients evaluated using both PESs were found to be very sensitive to the energy resolution of the reaction probability, especially at temperatures lower than 100 K. It is found that the rate coefficient remains largely constant in the temperature range of 10-39 K, in agreement with the conclusions of a recent experimental study [Carty et al., J. Phys. Chem. A 110, 3101 (2006)]. This is in contrast with the time-independent quantum calculations of Xu et al. [J. Chem. Phys. 127, 024304 (2007)] which, using the same PES, predicted nearly two orders of magnitude drop in the rate coefficient value from 39 to 10 K. Implications of our findings to oxygen chemistry in the interstellar medium are discussed.