A new ab initio potential energy surface for the collisional excitation of O2 by H2

Abstract

We present a new four dimensional (4D) potential energy surface for the O₂–H₂ system. Both molecules were treated as rigid rotors. Potential was obtained from the electronic structure calculations using a partially spin-restricted coupled cluster with the single, double and perturbative triple excitations [RCCSD(T)] method. The four atoms were described using the augmented correlation-consistent quadruple zeta (aug-cc-pVQZ) basis sets. Bond functions were placed at mid-distance between the O₂ center of mass and the center of mass of H₂ for a better description of the van der Waals interaction. Additionally, at five characteristic geometries, we calculated perturbational components of the interaction energy using the Symmetry-Adapted Perturbation Theory [SAPT] approach to explain the anisotropy of the potential energy surface. Bound states of the O₂–H₂ van der Waals complex are computed using this potential. Close coupling calculations of the inelastic integral cross sections of O₂ in collisions with para-H₂ and ortho-H₂ were also calculated at low energies. After Boltzmann thermal averaging, rate coefficients were obtained for temperatures ranging from 5 to 100 K. No significant differences exist between para- and ortho-H₂ results.