Specific features of the kinetics of H2-O2-O2(a 1Δ g ) mixtures: II. Quenching of O2(a 1Δ g ) excited in a discharge behind the shock front at temperatures of 500–1020 K

Abstract

Results of experiments on the quenching of singlet delta oxygen (SDO) O2(a 1Δ g ) in lean hydrogen-oxygen mixtures at temperatures of 500–1020 K and pressures of 26–90 Torr behind the shock front are analyzed theoretically. The processes affecting SDO quenching are simulated taking into account the temporal characteristics of the experiment and various mechanisms of energy transformation in an O2(a 1Δ g )-H2-H-HO2 system. It is demonstrated that the approximations of both fast and slow (in comparison with the vibrational relaxation time of the HO2 radical) quenching of the electronically excited state of the radical are in good agreement with the experimental data on the effective rate constant of SDO deexcitation at temperatures of up to 700 K. It is shown that the available data on the kinetics of reactions involving SDO in H2-O2-O2(a 1Δ g ) mixtures overestimate the SDO quenching rate in comparison with the experimental results obtained at temperatures above 850 K. The decrease in the rate constant of the reaction H + O2(a 1Δ g )→ products by one order of magnitude makes it possible to match the simulation results to the experimental data. The existence of the processes restoring SDO in the presence of atomic hydrogen that are not considered in the current models of the H2-O2-O2(a 1Δ g ) kinetics is supposed.