PRODUCT BRANCHING FRACTIONS IN THE REACTION OF NH (ND) ((3)SIGMA(-)) WITH NO

We have carried out a combined experimental and theoretical study of the reaction of NH (ND) ((3) Sigma(-)) With NO aimed at understanding the product distribution from that reaction. The reaction was studied at room temperature using the discharge flow technique with mass spectrometric detection of the reaction products. Measured product branching fractions at room temperature for production of N2O + H (D) were 0.8 +/- 0.4 for NH ((3) Sigma(-)) + NO and 0.87 +/- 0.17 for ND((3) Sigma(-)) + NO (l sigma statistical errors). Stationary points on the HNNO (2)A' potential energy surface were characterized using the Gaussian 2 ab initio method. The initial addition of NH((3) Sigma-) to NO on the (2)A' surface is predicted to proceed without a barrier to form trans-HNNO; reaction to produce the cis isomer is predicted to have a barrier of 2.9 kcal/mol. The cis- and trans-HNNO are predicted to be at -48.9 and -56.0 kcal/mol relative to the separated reactants. Transition states with energies of -25.3 and -17.9 kcal/mol were located for dissociation of the cis isomer into H + N2O and OH + N-2, respectively. The transition state for interconversion of the isomers was calculated to be at approximately -30.8 kcal/mol. The trans-HNNO was found to isomerize to the cis form before decomposing. The potential energy surface calculated explains the major features of the reaction.