Kinetics of the O(3P) + N2O Reaction. 1. Direct Measurements at Intermediate Temperatures

Rate coefficients for the consumption of O atoms by their reaction with N 2 O have been measured, at pressures from 130 to 500 mbar, using the high-temperature photochemistry technique. These represent the first direct measurements of k values of the reaction. The ground-state oxygen atoms were produced by laser photolysis of SO 2, or by flash photolysis of either SO 2 or O 2, and monitored by time-resolved resonance fluorescence. The results yield k (1075−1140 K) = 3.2 × 10 -11 exp(−9686 K / T ) cm 3 molecule -1 s -1 with 2σ precision limits of ±12% and corresponding 2σ accuracy limits of ±26%. Results from several sources in the literature indicate a high sensitivity of the O + N 2 O reaction system to traces of H 2 O, which increases the rates if present as a contaminant. For this reason, possible effects of traces of H 2 O on the results were modeled. Simulated decay curves with a hypothetical H 2 O contaminant were used as a test of the experimental data reduction procedures. Although the concentration of H 2 O needed to significantly affect the results is small, the amount that could have been present is even less and is shown to have had negligible effects. The results are in qualitative agreement with a recent T ≥ 1680 K shock tube study (D. F. Davidson, M. D. DiRosa, A. Y. Chang, and R. K. Hanson, ref 9) in that extrapolation of their results to the present temperatures indicates rate coefficients much larger than had been previously thought. However, though the results agree within error limits for such a long extrapolation, the present results are about a factor of 4 smaller. Combined with the results of the companion paper by Meagher and Anderson (ref 6, following paper in this issue), in which the prior literature is critically reevaluated, it is found that the O 2 + N 2 product channel dominates at the present temperatures.