Theoretical analysis of reaction kinetics with singlet oxygen molecules

Abstract

A comparative analysis of predictive ability of three approaches to estimate the rate constants of reactions of H₂, H, H₂O and CH₄ with electronically excited O₂(a¹Δ_g) and O₂(b¹Σ⁺_g) molecules is conducted. The first approach is based on a detailed ab initio study of potential energy surfaces. The second one is known as the “bond energy–bond order” method, and the third approach is a modification of the updated method of vibronic terms that makes it possible to evaluate the activation energy of reactions involving electronically excited species. The comparison showed that the estimates of the energy barrier by the updated method of vibronic terms for some reactions can be in good agreement with ab initio calculations and available experimental data. It was revealed that reactions of O₂(b¹Σ⁺_g) molecules with H₂, H₂O and CH₄ molecules and with the H atom result in the formation of electronically excited species. The reactivity of O₂(b¹Σ⁺_g) molecules is smaller than that of O₂(a¹Δ_g) ones, but much higher as compared to the reactivity of ground state O₂ molecules. For each reaction under study involving oxygen molecules in the excited electronic states O₂(a¹Δ_g) and O₂(b¹Σ⁺_g) the recommended temperature-dependent rate constants are presented.