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 up...