RATE CONSTANTS FOR THE THERMAL-DISSOCIATION OF N2O AND THE O(P-3)+N2OREACTION

The thermal dissociation of N2O in argon was investigated by monitorin g the formation of O(P-3) atoms in the reflected shock regime using at omic resonance absorption spectrophotometry (ARAS). The total density and [N2O] ranges were, (2.6 x 10(18))-(5.4 x 10(18)) molecules cm(-3) and (3.3 x 10(12))-(7.9 x 10(15)) molecules cm(-3), respectively. Valu es for the bimolecular rate constant (131 points), derived under low-p ressure limit conditions are given by the Arrhenius expression: k(1)(T ) = (1.18 +/- 0.16) x 10(-9) exp[(-57820 +/- 460 cal mol(-1))/RT] cm(3 ) molecule(-1) s(-1) for the temperature range, 1195 less than or equa l to T less than or equal to 2384 K. These results extend the low-temp erature range of ARAS measurements of k(1) by about 200 degrees C whic h is very significant in 1/T; and the value of the rate constant was e xtended by more than an order of magnitude. The present data were comb ined with previously published ARAS data to form a composite data set with a total of 278 points. Although systematic differences between th e data of the various groups were discernible, all the data are well r epresented by the following Arrhenius equation: k(1)(T) = (9.52 +/- 1. 07) x 10(-10) exp[(-57570 +/- 390 cal mol(-1))/RT] cm(3) molecule(-1) s(-1) for the temperature range, 1195 less than or equal to T less tha n or equal to 2494 K). Uncertainties in the Arrhenius expression are g iven at the one standard deviation level and the mean deviation of the experimental data from that predicted by the expression is +/-26%. Th ese results are compared to those from previous experimental studies, The rate of the reaction of O(P-3) with N2O was investigated experimen tally and by kinetic modeling, but only over a limited temperature ran ge, 1200 less than or equal to T less than or equal to 1400 K. Upper l imit values of the overall rate constant for the O(P-3) + N2O 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 t hree) than those calculated from the recommended Arrhenius expressions of Baulch et al. (1973), Hanson and Salimian (1984), and Tsang and He rron (1991).