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)=k_1d/(k_1a+k_1d) 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.