Potential energy surfaces for O + O2 collisions.

Abstract

We present global potential energy surfaces for nine adiabatic electronic states of O3, namely, 1 1A', 2 1A', 1 1A″, 1 3A', 2 3A', 1 3A″, 1 5A', 2 5A', and 1 5A″. These are the states of O3 that are accessed in electronically adiabatic collisions of a ground-state triplet O2 molecule with a ground-state triplet O atom. The surfaces are based on XMS-CASPT2 electronic structure calculations with dynamically scaled external correlation. The active space has 12 active electrons distributed in the nine 2p orbitals. The adiabatic surfaces are fitted to analytic functions using a many-body expansion where the pairwise additive term is fitted to an accurate diatomic potential including a damped dispersion term, and the many-body part, without disconnected terms, is fitted with permutationally invariant polynomials in mixed exponential-Gaussians to the electronic structure data points. The selection and weighting of points for the fits are designed to produce surfaces suitable for describing energy transfer and dissociation in high-energy collisions.