The Formation of OH*(2Σ+) Radical in the Reaction of Hydrogen with Oxygen behind a Shock Wave in Nonequilibrium Conditions

Abstract

The mechanism of formation of the electronically excited radical OH*(A2Σ+) has been studied by analyzing calculations quantitatively describing the results of shock wave experiments carried out in order to determine the moment of maximum OH* radiation at temperatures T < 1500 K and pressures P ≤ 2 atm in the H2 + O2 mixtures diluted by argon when the vibrational nonequilibrium is a factor determining the mechanism and rate of the overall process. In kinetic calculations, the vibrational nonequilibrium of the initial H2 and O2 components, the HO2, OH(X2Π), O2*(1Δ) intermediates, and the reaction product H2O were taken into account. The analysis showed that under these conditions the main contribution to the overall process of OH* formation is caused by the reactions OH + Ar → OH* + Ar, H2 + HO2 → OH* + H2O, H2 + O*(1D) → OH* + H, HO2 + O → OH* + O2 and H + H2O → OH* + H2, which occur in the vibrational nonequilibrium mode (their activation barrier is overcome due to the vibrational excitation of reactants), and by H + O3 → OH* + O2 and H + H2O2 → OH* + H2O, which are reverse to the reactions of chemical quenching.