Kinetics of the Reactions of N(⁴S) Atoms with O₂ and CO₂ over Wide Temperatures Ranges

Abstract

Rate coefficients for the depletion of ground-state nitrogen atoms by O2 have been measured using a high-temperature photochemistry reactor. The N atoms were generated by VUV flash photolysis of N2O, and the relative concentrations were monitored by resonance fluorescence. The data are best fitted by the expression k(400−1220 K) = 2.0 × 10-18(T/K)2.15 exp(−2557 K/T) cm3 molecule-1 s-1 with 2σ precision limits varying from ±7% to ±20% depending upon temperature, and corresponding 2σ accuracy limits of ±23% to ±30%. Good agreement is found with earlier, electrical discharge initiated, rate coefficient measurements for the 280−910 K domain. Semiempirical theory-based calculations are presented that lead to a plot nearly indistinguishable from those of the present results and the Baulch et al. recommendation for the 300−5000 K temperature range. These yield a classical barrier E0⧧ of 27.4 kJ mol-1. No reaction with CO2 could be observed; upper limit rate coefficients were obtained from 285 to 1140 K. These upper limits indicate that the reverse reaction is insignificant for models of nitrate ester and nitramine propellant dark zones.