High-Energy Reaction Dynamics of N$_{3}$

TL;DR

This study investigates the reaction dynamics of N$_3$ formation and dissociation using advanced computational methods, providing new insights into reaction rates, mechanisms, and the lifetime of N$_3$ with implications for atmospheric chemistry.

Contribution

The paper introduces a RKHS-based global PES for N$_3$ reactions and compares it with other PESs, also developing neural network models for reaction dynamics exploration.

Findings

Computed thermal rates match experimental data for atom exchange.

RKHS-PES overestimates atomization rates, while PIP-PES aligns better with experiments.

Estimated N$_3$ lifetime is approximately 200 femtoseconds.

Abstract

The atom-exchange and atomization dissociation dynamics for the N($^4$S) + N$_2(^1 \Sigma_{\rm g}^+)$ 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 $({\rm N_A N_B} + {\rm N_C} \rightarrow {\rm N_A N_C} + {\rm N_B}$), 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$(^4{\rm S})$ 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 N$_3$ molecule is estimated to be $\sim 200$ 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.