Journal of Physical Chemistry A, Vol.102, No.18, 3175-3183, 1998
Theoretical study of the H-2+NO and related reactions of [H2NO] isomers
Mechanisms of the reactions occurring on the multichannel lowest doublet potential energy surface of the [H2NO] system containing H2NO, HNOH, and NOH2 intermediates and including the H-2 + NO, NH2 + O, NH + OH, and H + HNO entry channels have been probed using unrestricted coupled-cluster formalism. Also, the transition structure on the doubler energy surface for the direct hydrogen abstraction from H-2 + NO yielding H + HNO has been identified. The energetic and molecular parameters derived from coupled cluster singles and doubles with triples correction (CCSD(T)) calculations using the 6-311++G(3df,3pd) basis set, based on their respective optimized geometries obtained with a 6-311++G(d,p) basis set, have then been utilized to compute the apparent rate constants of the different competitive channels in the [H2NO] system within the framework of a quantum version of Rice-Ramsperger-Kassel theory (QRRK). The Hz + NO reaction is found to be a rather slow reaction, and it occurs via bimolecular hydrogen abstraction. The calculated total rate constant for this reaction at 2000 K and 1 atm is 2.35 x 10(8) cm(3) mol(-1) s(-1). Stabilization of NH2O or NHOH intermediates plays a minor role in the kinetics of NH2 + O reaction which is dominated by the dissociation products, HNO + H, NH + OH and H-2 + ND. The H + HNO reaction kinetics has only 10% contribution from addition/isomerization/dissociation paths at 2000 K and 1 atm. H? + NO and H + HNO are expected to be the competitive products in the reaction of OH with nitrene. The calculated standard heats of formation are Delta H-f(298)(NH2O) = 17.5 +/-2 and Delta H-f(298)(HNOH) = 23.7 +/- 2 kcal/mol.
Keywords:RAMSPERGER-KASSEL ANALYSIS;POTENTIAL-ENERGY SURFACES;STATE THEORY CALCULATIONS;RADICAL REACTIONS;RATE CONSTANTS;HYDROGEN;NH2;DECOMPOSITION;MOLECULES;ABINITIO