Molecular recombination dynamics of nitrogen from quasi-classical trajectory simulations of the N₃ system

The dynamics and the kinetics of the recombination of molecular nitrogen is investigated using the quasiclassical trajectory calculations of the N₃ system described by the ab initio potential energy surface (PES) developed at University of Minnesota. The main reaction pathways considered include the direct mechanism which is characterized by a simultaneous interaction of the three atoms and a two-step binary collision (TSBC) mechanism which is characterized by the formation and subsequent stabilization of an intermediate. The latter can be further classified as Lindemann or Chaperon mechanism based on the role played by the third body. All three pathways are treated equally by introducing a time lag parameter. The recombination rate coefficients are evaluated using a novel expression developed for three body collisions and the internal energy distributions are investigated. The rate coefficients agree well with those expected from detailed balance and the dissociation rate coefficients. Low temperature recombination rate coefficients which are difficult to obtain using detailed balance are evaluated at a low computational cost. The presence of the three mechanisms have been identified by studying the recombination trajectories and the dependence of the recombination probability on the impact parameters of the collision. The direct mechanism has a higher probability for a recombination event compared to the TSBC mechanism, but ultimately has a low rate coefficient due to the dynamics of the mechanisms.