Pressure-dependent kinetic analysis of the NH potential energy surface.

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