Low-Temperature Thermal Rate Constants for the Water Formation Reaction H2 +OH from Rigorous Quantum Dynamics Calculations.

Thermal rate constants for the prototypical water-forming reaction H2 +OH→H+H2 O were obtained for temperatures between 150 K and 600 K by rigorous quantum dynamics calculations including all degrees of freedom. Results are reported for a recent, highly accurate neural network potential (NN1) and compared to results obtained on a previous, semi-empirical potential (SE). The rate constants computed on both potentials significantly differ in their temperature dependence, and differences of over one order of magnitude in the rates were found. The rate constants computed for the NN1 potential compare very well to experimental work. Furthermore, the influence of overall rotation is discussed for the title reaction. While previous close-coupling simulations were limited to thermal rate constants above room temperature, we report rate constants for temperatures as low as 250 K. The high-level results reported here provide an accurate benchmark for the development of approximate methods for the calculation of thermal as well as microcanonical rate constants.