THE DECOMPOSITION OF NITROUS-OXIDE AT LESS-THAN-OR-EQUAL-TO-P-LESS-THAN-OR-EQUAL-TO-10.5 ATM AND ESS-THAN-OR-EQUAL-TO-T-LESS-THAN-OR-EQUAL-TO-1173K

Reaction experiments on mixtures of N2O/H2O/N-2 were performed in a va riable pressure flow reactor over temperature, pressure, and residence time ranges of 1103-1173 K, 1.5-10.5 atm, and 0.2-0.8 s, respectively . Mixtures of approximately 1% N2O in N-2 were studied with the additi on of varying amounts of water vapor, from background to 3580 ppm. Exp erimentally measured profiles of N2O, O-2, NO, NO2, H2O, and temperatu re were compared with predictions from detailed kinetic modeling calcu lations to assess the validity of a reaction mechanism developed from currently available literature thermochemical and rate constant parame ters. Sensitivity and reaction flux analyses were performed to determi ne key elementary reaction path processes and rates. Reaction rate con stants for the uni-molecular reaction, N2O --> N-2 + O, were determine d at various pressures in order to match overall experimental and nume rical decomposition rates of N2O. The numerical model included a newly determined rate constant for N2O + OH --> HO2 + N-2 with an upper lim it of 5.66 x 10(8) cm(3) mol(-1) sec(-1) at 1123 K. This is considerab ly smaller than presently reported in the literature. The experimental ly observed rate of N2O decomposition was found to be slightly depende nt on added water concentration. The rate constant determined for the elementary decomposition is strongly dependent on the choice of rate c onstants for the N2O + O double left right arrow N-2 + O-2 and N2O + O double left right arrow NO + NO reactions. In the absence of accurate data at the temperatures of this work, and based on these and other e xperiments in this laboratory, we presently recommend rate constants f rom the review of Baulch et al. The basis for this recommendation is d iscussed, including the impact on the rate constants derived for eleme ntary nitrous oxide decomposition. The uncertainties in the rate const ants as reported here are +/-30%.The present mechanism was applied to previously reported high-pressure shock tube data and yields a high-pr essure limit rate constant a factor of three larger than previously re ported at these temperatures. The following expressions for the elemen tary decomposition reaction are recommended: k(0), N-2 = 9.13 x 10(14) exp(-57,690/RT) cm(3) mol(-1) s(-1) and k(x) = 7.91 X 10(10) exp(-560 20/RT) s(-1). Simple Lindemann fits utilizing these parameters reprodu ce the pressure dependent rate constants measured here within +/-25%. (C) 1995 John Wiley and Sons, Inc.