Pressure-Dependent Kinetic Analysis of the N2H3 Potential Energy Surface

Abstract

Pressure-dependent reactions on the N2H3 potential energy surface (PES) are studied at the CCSDT(Q)/aug-cc-pVTZ level of theory. This work extends the N2H3 PES relative to previous literature studies by adding another isomer, NH3N, and additional bimolecular channels adjacent to the new isomer, NNH + H2, and H2NN + H. Theoretical predictions are made for the rate coefficients of all path and well-skipping pressure-dependent reactions. The theoretical analyses employ a combination of ab-initio transition state theory and master equation simulations. Pressure-dependent rate coefficients are computed for all reactions in the network. The dominant products of NH2 + NH(T) recombination are N2H2 + H, and at high pressures and low temperatures N2H3 formation becomes important. Collisions of H2NN + H on this surface yield mainly N2H2 + H as well. Important secondary reactions are H2NN + H <=> NNH + H2 at high temperatures and all examined pressures and H2NN + H <=> N2H3 at low temperatures and high pressures. None of these three reactions were considered by previous NH3 oxidation models with pressure-dependent rate coefficients. The rate coefficients obtained here should be useful in modeling ammonia, hydrazine, and hydrazine derivatives in various combustion environments.