Production of metastable singlet oxygen in the reaction of nitric oxide with active oxygen

Predictive modeling of the performance of EOIL laser systems must address the kinetics of the active oxygen flow, including the production of O 3 from recombination of O and O 2 , and the effects of NO as an additive to remove O and promote O 2 (a) formation. This paper describes experimental measurements of the reaction kinetics for active-oxygen flows generated by microwave discharge of O 2 /He mixtures at 3 to 10 torr. The concentrations of O 2 (a 1 Δ), O, and O 3 were directly measured as functions of reaction time in a discharge-flow reactor. Both the O removal rate and the O 3 production rate were observed to be significantly lower than expected from the widely accepted three-body recombination mechanism for O 3 production, indicating the existence of a previously unknown O 3 dissociation reaction. Addition of NO to the flow well downstream of the discharge resulted in readily detectable production of O 2 (a) in addition to that generated by the discharge. The observed O2(a) production rates were remarkably insensitive to variations in total pressure, O 2 concentration, and NO concentration over the ranges investigated. The mechanism for this O 2 (a) production remains to be identified, however it appears to involve a hitherto undetected, metastable, energetic species produced in the active-oxygen flow.