Potential energy surfaces for the low-lying 2A″ and 2A′ States of HO2: Use of the diatomics in molecules model to fit ab initio data

Abstract

A DIM (diatomics in molecules) model utilizing a large basis set (34 2A″ and 32 2A′ states) was used to obtain the potential energy surfaces relevant to the chemical reaction H+O2→OH+O. The ground state, 12A″, surface was fitted to 910 accurate ab initio points of Walch et al. [J. Chem. Phys. 94, 7068 (1991)]. The resulting fit accurately describes the C2v conical intersection in the regions for which ab initio data are available, and the linear conical intersection is accurately described in the H+O2 region. It is also an accurate global fit with an rms deviation of 0.096 eV (2.22 kcal/mol). The behavior of the low-lying excited states, 12A′, 22A″, and 22A′, appears to be qualitatively correct everywhere and quantitative near the low-lying conical intersections. The DIM formulation allows the computation of the gauge potential relevant for the description of the geometric phase and non-adiabatic effects in multi-surface reactive scattering calculations.