An ab initio potential energy surface for the study of rotationally inelastic OH–H2 collisions

A new two-configuration self-consistent field (SCF) plus dispersion potential for the interaction of OH with H2 is presented. The ground state of OH is a 2Π state leading to a two component potential which is diagonal in the adiabatic electronic basis in which the quantum chemical calculations are done. The transformation between the adiabatic basis and the electronic basis used in collision calculations is described. The transformed potential matrix is Hermitian in this electronic basis when OH–H2 configurations with no plane of symmetry are considered. The orientation dependence of the elements of the potential matrix is given in the form of a spherical expansion and the results are compared with previous potential calculations. The comparison is discussed in terms of the dependence on the orientation of the H2 molecule.