A kinetic study of the reaction of NH2 with NO in the temperature range 1400–2800 K

Abstract

The reaction (1) NH2+NO→products was investigated behind incident and reflected shock waves in the temperature range 1400–2800 K and densities ranging from 1.4 to 20×10-6 mol cm-3. The source of NH2 radicals was the thermal dissociation of hydrazine (N2H4). Time histories of NH2 (597.365 nm), NH (336.100 nm) and OH (308.417 nm) were detected by narrow linewidth laser absorption. The H and O atom formations were followed by means of atom resonance absorption spectroscopy (ARAS) at 121.5 nm and 130.5 nm. In addition, NH2 radicals were detected at very low concentrations using very sensitive frequency modulated (FM) spectroscopy. For the overall rate constant k1 in the temperature range 1400–2200 K an Arrhenius expression of k1=1.3×1013×exp(-35 kJ mol-1/RT) cm3 mol-1 s-1 (±60%) was determined. In connection with previous literature data a minimum of the overall rate constant was found around 1200 K. According to several other investigations, the reaction channel (1a) NH2+NO→N2+H2O clearly dominates the channel (1d) NH2+NO→N2+OH+H at temperatures lower than 1000 K. At room temperature a branching ratio α(T)=k1d/(k1a+k1d) of around 10% is reported. Our investigations of the products H and OH of the channel (1d) and the determination of the branching ratio show that the contribution of channel (1d) increases from around 50% at 1500 K to 80% at 2800 K. The other reaction channels investigated, (1c) leading to N2O+H2 and (1g) to HNO+NH, are of minor importance.