Selective product channels in the reactions of NH(<i>a</i> 1Δ) and NH(<i>X</i> 3Σ−) with NO

Abstract

Reactions of imidogen, NH, in the electronically excited a 1Δ and ground X 3Σ− states with NO have been studied at 300±2 K and at 20 Torr (Ar). NH(a 1Δ) and NH(X 3Σ−) were produced in the 193 nm photolysis of HNCO and CHBr3/NO, respectively, and detected by the laser-induced fluorescence (LIF) technique. Rate constants have been measured under pseudo-first-order conditions by scanning the time delay between the photolysis and probe laser pulses. Overall rate constants were determined: [4.8±0.1(2σ)]×10−11 cm3 molecule−1 s−1 for NH(a 1Δ)+NO; [4.7±0.6(2σ)]×10−11 cm3 molecule−1 s−1 for NH(X 3Σ−)+NO. The ratio of electronic quenching, NH(a 1Δ)+NO→NH(X 3Σ−) +NO, to the overall reaction has been obtained to be 0.53±0.1. An interesting specificity for the products from different spin states of the reactants has been found from observation of OH concentration profiles. NH(X 3Σ−)+NO produces OH+N2 exclusively, while NH(a 1Δ)+NO is over five times less effective in producing OH+N2. Profiles of H atoms detected by the vuv LIF technique indicated that H atoms are directly produced in the reaction NH(a 1Δ)+NO but not in the reaction NH(X 3Σ−)+NO.