Direct ab initio dynamics studies of vibrational-state selected reaction rate of the OH1H2 ̃H1H2O reaction

We present direct ab initio dynamics studies of vibrational-state selected reaction rates of the OH1H2→H1H2O reaction. Rate constants for both the OH1H2~v51! and OH~v51!1H2 reactions were calculated based on a full variational transition state theory plus multidimensional semiclassical tunneling approximations within a statistical diabatic model. The potential energy surface information was calculated at an accurate level of molecular orbital theory. In particular, geometries and frequencies along the minimum energy path were calculated at the quadratic configuration interaction level including all single and double excitations ~QCISD! with the 6-3111G(d ,p) basis set. Energies along the minimum energy path were further improved by a series of single point projected fourth-order Möller–Plesset perturbation theory ~PMP4! calculations using the 6-31111G(2d f ,2pd) basis set. Our present results of vibrational excited state rate enhancements agree very well with previous experimental data. In view of these results, we also discuss the accuracy of the Schatz–Elgersma potential energy function in more detail. © 1995 American Institute of Physics.