A Shock Tube Study of the Product Branching Ratio of the NH_2 + NO Reaction at High Temperatures

摘要

The product branching ratio of NH_2 + NO → N_2 + H_2O 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 NH_2 radical was measured using a frequency modulation absorption technique. The initial gas mixture compositions were 8-28 ppm monomethylamine (CH_3NH_2), 0.4-1.2% ammonia (NH_3), and 0.4% NO, and the balancer Ar. According to sensitivity analysis using a detailed 125-reaction mechanism, the NH_2 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, k_1 = 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.