SHOCK TUBE DETERMINATION OF THE OVERALL RATE OF NH_2 + NO → PRODUCTS AT HIGH TEMPERATURES

摘要

The rate coefficient of the reaction NH_2 + NO→ products (Rl) was determined in shock tube experiments using frequency modulation absorption spectroscopy for detection of NH_2. Due to the sensitivity of the diagnostic system, very low reactant concentrations could be employed to reduce the influence of secondary reactions on the NH_2 profiles. The source of the NH_2 radicals in the experiments was the thermal decomposition of CH_3NH_2. To determine κ_1, a perturbation strategy was employed that is based on changes in the NH_2 profiles when NO is added to the CH_3NH_2/Ar mixtures. Analysis showed that NH_2 profiles in the CH_3NH_2/NO/Ar mixtures were sensitive primarily to reaction Rl, with significantly lower sensitivity to the branching ratio and other NH_2 reactions. The measured NH_2 profiles were interpreted by detailed kinetic modeling to obtain k_1 values in the temperature range 1716― 507 K. The present κ_1 values are consistent with recent theoretical results of Miller and coworkers. There is no evidence for a positive activation energy for this reaction at elevated temperatures as reported in several other high-temperature experimental studies. Combining the present high-temperature data with lower temperature determinations yields the following simple expression for the overall reaction rate, κ_1 = 2.08 X 10~(16) T~(―1.34) cm~3/mol s for the temperature range 300―2500 K.