Reactions of NH2 with NO2 and of OH with NH2O

The reaction system produced by 193 nm flash photolysis of a mixture of NH3 and NO2 has been investigated experimentally and modeled. The accepted bel ief that only two channels are of significance for the reaction between NH2 and NO2, producing (a) N2O and H2O and (b) NH2O and NO, is confirmed by th e absence of H2O2 absorption signals and the absence of early HNO, as H2O2 and HNO are produced by two of the possible five NH2 + NO2 channels. The fa ct that the OH concentration extrapolated to the flash is less than the ini tial NH2 concentration indicates that the channel producing two OH molecule s is not significant. HNO is observed to be produced on a slower time scale than that of the NH2 + NO reaction and is believed to be formed by the rea ction of OH with NH2O (OH is formed by the reaction of NO2 with H produced by the flash photolysis of NH3). NH2O does not appear to react with NO2 at 296 K on our time scale. Modeling of the reaction system gives a rate for t he reaction between NH2O and OH of 1.8(10) x 10(-10) cm(3) s(-1). An excess continued decay of OH at long times after NH2O has virtually disappeared c an be accounted for by reaction of OH with HNO with a rate in the range (2- 8) x 10(-1) cm3 s(-1).