A COMPREHENSIVE STUDY OF THE REACTION NH2-]PRODUCTS - REACTION-RATE COEFFICIENTS, PRODUCT BRANCHING FRACTIONS, AND AB-INITIO CALCULATIONS(NO)

We have undertaken a comprehensive study of the reaction NH2((XB1)-B-2 ) + NO --> N-2 + H2O (1a) and NH2(X B-2(1)) + NO --> N2H + OH --> N-2 + H + OH (1b). Experimental measurements of the reaction rate coeffici ent and product branching fraction are combined with accurate ab initi o calculations to give a detailed picture of this important reaction. The rate constant of reaction 1 was investigated in the temperature ra nge 203 K less than or equal to T less than or equal to 813 K using th e laser photolysis/CW laser-induced fluorescence technique for product ion and detection of NH2. The rate coefficient was found to be pressur e independent between 10 and 100 Torr and is well described by k(1)(T) = 1.65 x 10(-7)T(-154)exp (-93 K/T) cm(3)/(molecule.s). The deuterium kinetic isotope effect for the reactions of NH2 and ND2 with NO was i nvestigated at temperatures between 210 and 481 K. A small, temperatur e-independent isotope effect of k(H)/k(D) 1.05 +/- 0.03 was found. Add itional experimental work focused on measuring the product branching f raction for production of OH, Phi(lb), and its deuterium isotope effec t at room temperature. Measurements were performed using the discharge flow technique with mass spectrometric detection of products. OH from channel Ib was reacted with excess CO and measured as CO2. The room t emperature branching fraction was measured as Phi(lb) = 9.0 +/- 2.5% ( NH2 +/- NO; T = 298 K) and Phi(lb) = 5.5 +/- 0.7% (ND2 + NO; T = 298 K ). Theoretical calculations have characterized the stationary points o n the potential energy surface connecting reactants with products usin g G2 and G2Q levels of theory. These calculations support the experime ntally observed temperature dependences and kinetic isotope effects.