Rotationally inelastic and hyperfine resolved cross sections for OH–H2 collisions. Calculations using a new <i>ab</i> <i>initio</i> potential surface

Abstract

Cross sections and rate constants are presented for the rotational excitation of OH in collision with ortho and para-H2, using a new ab initio interaction potential [Offer and Van Hemert, J. Chem. Phys. 99, 3836 (1993)]. The cross sections are given at a number of energies and are compared with those calculated using an earlier potential energy surface, and with the available experimental results. A strong oscillatory behavior is found in the cross sections for collisions with ground state para-H2 which was not apparent in earlier calculations. The oscillatory behavior is very much reduced in collisions with ortho-H2. Rate constants obtained by averaging the cross sections over a Maxwell–Boltzmann velocity distribution are given at a temperature of 300 K. Expressions for calculating the hyperfine resolved cross sections by transforming the S-matrices are discussed for the case where H2 is no longer constrained to its rotational ground state, and cross sections for transitions between the hyperfine resolved levels are given for collisions with both para and ortho-H2.