Product branching fractions in the reactions of NH(a 1Δ) and NH(X 3Σ−) with NO

Abstract

Reactions of the imidogen radical NH with NO have been investigated in its electronically excited a 1Δ and ground X 3Σ− states, where UV- and VUV-LIF were used to monitor radical and atomic species in the 193 nm photolysis of HNCO/NO mixtures at 295±3 K in 20 Torr He. The rate constants for the reactions of NH(a 1Δ; v=0,1)+NO→products (1) and NH(X 3Σ−; v=0,1)+NO→products (2) were determined. No apparent effect on the rate constants of the vibrational excitation of NH was observed in either reaction. H and OH were observed as products in both reactions, whereas physical quenching of NH(a 1Δ) to NH(X 3Σ−) is dominant in Reaction (1). In addition, O(3P) was found to be produced in Reaction (1) for the first time. Product branching fractions in these reactions were determined using proper reference reactions, along with addition of Xe to control the relative contributions of Reactions (1) and (2). The branching fractions in Reaction (1) were: 0.57 for quenching (1a), 0.20 for H+N2O (1b), 0.14 for OH+N2 (1c), 0.08 for the sum of O+N2H (1d), and O+N2+H (1e), and in Reaction (2): 0.65 for H+N2O (2a), 0.30 for OH+N2 (2b). These results were found to be consistent with former theoretical predictions that Reactions (1) and (2) produced on the same doublet surfaces. It was elucidated that the observed delay of OH(v=0) production was due to the vibrational relaxation of OH(v≥1) produced in the reactions.