Rate Constants for the Thermal Dissociation of N2O and the O(3P) + N2O Reaction

The thermal dissociation of N 2 O in argon was investigated by monitoring the formation of O( 3 P) atoms in the reflected shock regime using atomic resonance absorption spectrophotometry (ARAS). The total density and [N 2 O] ranges were, (2.6 × 10 18 )−(5.4 × 10 18 ) molecules cm -3 and (3.3 × 10 12 )−(7.9 × 10 15 ) molecules cm -3, respectively. Values for the bimolecular rate constant (131 points), derived under low-pressure limit conditions are given by the Arrhenius expression: k 1 ( T ) = (1.18 ± 0.16) × 10 -9 exp[(−57820 ± 460 cal mol -1 )/ RT ] cm 3 molecule -1 s -1 for the temperature range, 1195 ≤ T ≤ 2384 K. These results extend the low-temperature range of ARAS measurements of k 1 by about 200 °C which is very significant in 1/ T; and the value of the rate constant was extended by more than an order of magnitude. The present data were combined with previously published ARAS data to form a composite data set with a total of 278 points. Although systematic differences between the data of the various groups were discernible, all the data are well represented by the following Arrhenius equation: k 1 ( T ) = (9.52 ± 1.07) × 10 -10 exp[(−57570 ± 390 cal mol -1 )/ RT ] cm 3 molecule -1 s -1 for the temperature range, 1195 ≤ T ≤ 2494 K). Uncertainties in the Arrhenius expression are given at the one standard deviation level and the mean deviation of the experimental data from that predicted by the expression is ±26%. These results are compared to those from previous experimental studies. The rate of the reaction of O( 3 P) with N 2 O was investigated experimentally and by kinetic modeling, but only over a limited temperature range, 1200 ≤ T ≤ 1400 K. Upper limit values of the overall rate constant for the O( 3 P) + N 2 O reaction were estimated by a statistical technique. These values were about a factor of 10 lower (with an overall uncertainty of about a factor of three) than those calculated from the recommended Arrhenius expressions of Baulch et al. (1973), Hanson and Salimian (1984), and Tsang and Herron (1991).