Rotational effects in the H2+OH→H+H2O reaction rate:: Full-dimensional close-coupling results

The dependence of the thermal rate constant of the H-2+OH --> H+H2O reaction on the rotational motion is investigated. Full-dimensional quantum calculations accurately accounting for the overall rotation, i.e., close-coupling (CC) calculations, are presented. These calculations are based on a flux correlation function approach and employ a rigorously correct statistical sampling scheme for the rotational degrees of freedom and the multi-configurational time-dependent Hartree (MCTDH) approach for the wavefunction propagation. They provide a first strictly correct description of the rate constant of the title reaction on the Schatz-Elgersma potential energy surface. The results are compared to approximate results obtained within the centrifugal sudden or coupled states (CS) approximation and the J-shifting approximation. No significant differences have been found between the accurate results and rate constants obtained within the CS approximation. In contrast, the J-shifting approximation overestimates the accurate results by 38% to 44% for temperatures between 300 K and 700 K. Reasons for the inaccuracy of the J-shifting approximation are discussed in detail. (C) 2000 American Institute of Physics. [S0021-9606(00)00238-5].