Pressure-dependent kinetic analysis of the N2H3 potential energy surface†

Abstract

The pressure-dependent reactions on the N₂H₃ potential energy surface (PES) have been investigated using CCSD(T)-F12/aug-cc-pVTZ-F12//B2PLYP-D3/aug-cc-pVTZ. This study expands the N₂H₃ PES beyond the previous literature by incorporating a newly identified isomer, NH₃N, along with additional bimolecular reaction channels associated with this isomer, namely NNH + H₂ and H₂NN(S) + H. Rate coefficients for all relevant pressure-dependent reactions, including well-skipping pathways, are predicted using a combination of ab initio transition state theory and master equation simulations. The dominant product of the NH₂ + NH(T) recombination is N₂H₂ + H, while at high pressures and low temperatures, N₂H₃ formation becomes significant. Similarly, collisions involving H₂NN(S) + H predominantly produce N₂H₂ + H. Secondary reactions such as H₂NN(S) + H ⇌ NNH + H₂ and H₂NN(S) + H ⇌ NH₂ + NH(T) are found to play a significant role at high temperatures across all examined pressures, while H₂NN(S) + H ⇌ NH₃N becomes prominent only at high pressures. Notably, none of these four H₂NN(S) reactions have been included with pressure-dependent rate coefficients in previous NH₃ oxidation models. The rate coefficients reported here provide valuable insights for modeling the combustion of ammonia, hydrazine, and their derivatives in diverse environments.