High-Energy Reaction Dynamics of N₃

The atom-exchange and atomization dissociation dynamics for the N(⁴S) + N₂(¹ Σg⁺) reaction is studied using a reproducing kernel Hilbert space (RKHS)-based, global potential energy surface (PES) at the MRCI-F12/aug-cc-pVTZ-F12 level of theory. For the atom exchange reaction ( NA NB + NC → NA NC + NB), computed thermal rates and their temperature dependence from quasi-classical trajectory (QCT) simulations agree to within error bars with the available experiments. Companion QCT simulations using a recently published CASPT2-based PES confirm these findings. For the atomization reaction, leading to three N(⁴ S) atoms, the computed rates from the RKHS-PES overestimate the experimentally reported rates by one order of magnitude whereas those from the PIP-PES agree favourably, and the T-dependence of both computations is consistent with experiment. These differences can be traced back to the different methods and basis sets used. The lifetime of the metastable N₃ molecule is estimated to be ~ 200 fs depending on the initial state of the reactants. Finally, neural network-based exhaustive state-to-distribution models are presented using both PESs for the atom exchange reaction. These models will be instrumental for a broader exploration of the reaction dynamics of air.