A shock tube study of the product branching ratio of the NH₂ + NO reaction at high temperatures

The product branching ratio of NH₂ + NO → NNH + OH and NH₂ + NO → N₂ + H₂O has been determined in the temperature range 1826-2159 K in a shock tube study. The pressure range behind reflected shock waves was 1.10 to 1.21 bar. The time history of the NH₂ radical was measured using a frequency modulation absorption technique. The initial gas mixture compositions were 8-28 ppm monomethylamine (CH₃NH₂), 0.4-1.2% ammonia (NH₃), and 0.4% NO, and the balance Ar. According to sensitivity analysis using a detailed 125-reaction mechanism, the NH₂ profiles are mainly sensitive to the branching ratio α = k_1a/(k_1a + k_1b) under the experimental conditions of this study, and they exhibit only a small sensitivity to secondary reactions and the overall rate coefficient, k₁ = k_1a + k_1b. The branching ratio increases from 0.59 ± 0.02 at 1826 K to 0.66 ± 0.04 at 2159 K. These results are consistent with our earlier measurements of the branching ratio at lower temperature and agree with the theoretical result of Miller and Klippenstein.