KINETIC-STUDIES OF NHX RADICAL REACTIONS

Combined experimental and theoretical studies of the reactions NH2(X2B1) + NO --> products (1) NH/ND(3SIGMA-) + NO --> products (2) and NH2(X2B1) + O --> products (3) were carried out in the present work. The rate constant of reaction (1) was investigated in the temperature range 293 K less-than-or-equal-to T less-than-or-equal-to 612 K using the laser photolysis continuous-wave laser-induced fluorescence technique for the production and detection of NH2. The results are well described by k1(T) = 5.43 X T-4.02 exp(-1034K/T) cm3 molecule-1 s-1. Stationary points on the potential energy surface were characterized using the GAUSSIAN-2 (G2) ab initio method. The surface is complex, with hydrogen-atom transfers and cis-trans isomerizations connecting five stable adduct species. The product distribution of reaction (2) was studied at room temperature using the discharge flow technique with mass spectrometric detection of the reaction products. Measured branching fractions for the production of N2O+H(D) were k2a/k2 = 0.84+/-0.4 for NH+NO and k2a/k2 = 0.87+/-0.17 for ND+NO. Stationary points on the ground 2A' surface were calculated using the G2 method. The transition state energy for the dissociation of the cis isomer into H+N2O was found to be lower than the transition state energy for dissociation into OH+N2. Additionally, trans-HNNO was found to isomerize to cis-HNNO before dissociation. For reaction (3), the molecular properties of all relevant intermediates and transition states on the ground state potential energy surface were determined using the G2 method. The results predict the formation of three intermediates, H2NO, trans-HNOH and cis-HNOH, all exothermic relative to the reactants. The transition states separating these intermediates from one another and their products (H-2+NO, H+HNO(1A') or NH+OH) were also characterized, several for the first time.