Theoretical Study of the H2 + NO and Related Reactions of [H2NO] Isomers

Abstract

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 H2 + NO, NH2 + O, NH + OH, and H + HNO entry channels have been probed using unrestricted coupled-cluster formalism. Also, the transition structure on the doublet energy surface for the direct hydrogen abstraction from H2 + 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 H2 + 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 × 108 cm3 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 H2 + NO. The H + HNO reaction kinetics has only 10% contribution from addition/isomerization/dissociation paths at 2000 K and 1 atm. H2 + 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 ΔHf298(NH2O) = 17.5 ± 2 and ΔHf298(HNOH) = 23.7 ± 2 kcal/mol.