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.