Computational study on detailed kinetics of HO2 + No reaction

Abstract

The reaction between two radicals HO2 and NO has a center role to play in both atmospheric and combustion chemistry, relevant to environmental concerns. In this work, ab initio molecular orbital calculations at different high levels of theory were used to investigate the mechanism for the reaction between HO2 and NO radicals. The rigorous singlet potential energy surface (PES) was constructed at accurate composite CBS-QB3 and W1U levels, which illustrates the three possible pathways for the formation of OH + NO2 from HO2 + NO either direct dissociation of the peroxynitrous acid, HOONO intermediate, or split reaction after the isomerization of HOONO to nitric acid (HNO3) or direct O abstraction reaction. Due to high activation barriers, the formation of HNO + O2, HON + O2, HONO + O, and direct abstractions of reactants are energetically unfavorable reactions. With the help of state-of-the-art Multi-Species Multi-Channel (MSMC) code [1], thermodynamic properties as well as the rate constants for the title reaction were also computed and analyzed at T = 300-2000 K and P < 76000 Torr. The good agreement of the predicted values in this study with experiment data can be applied to an improvement of the engine efficiency and air quality modeling. Keywords: combustion chemistry, atmospheric chemistry, thermodynamics, rate constants, CBS-QB3, W1U method.