QUANTUM REACTIVE SCATTERING OF 4-ATOM REACTIONS WITH NONLINEAR GEOMETRY - OH+H-2-]H2O+H

A quantum mechanical method is described for calculating state-selected cross sections and rate constants for four-atom reactions of the general form AB + CD --> ABC + D with nonlinear geometry. The method involves using hyperspherical coordinates to describe the BC and CD bonds, accounting for both the rotation of the AB molecule and the bending mode of the ABC molecule with a spherical harmonic basis set, holding the AB spectator bond length fixed and applying a version of the bending-corrected-rotating line approximation to treat the rotation of the CD molecule. The method is applied to the OH(j) + H-2(v) --> H2O(n,m) + H reaction, and its reverse reaction, where v and j are vibrational and rotational quantum numbers, and n and m label bending and local OH-stretching vibrational states of the H2O molecule. A modified potential energy surface based on a fit to ab initio data is used. Comparisons of the calculated cross sections are made with quasiclassical trajectory calculations. The effect of the bending and stretching modes of the H2O molecule on the reaction is examined in detail. The calculated rate constants for the OH + H-2 reaction agree very well with experiment over the whole temperature range of 250-1050 K.