Quasiclassical trajectory analysis of nitrogen for high-temperature chemical kinetics

Understanding gas–phase chemical kinetics is important for modeling hypersonic flows. This paper discusses quasiclassical trajectory analysis, in which gas–phase interactions are simulated using ab initio quantum chemistry data. N₂ N₂, N₂ N, and N₂ O₂ collisions are studied for conditions at thermal equilibrium and nonequilibrium. The nitrogen dissociation rate with all collision partners is found to be similar for a given thermal environment: the largest deviation is 50% at thermal nonequilibrium, and at equilibrium the N₂ N₂ and N₂ N rates are within 15% of each other. The vibrational energy decrease due to nitrogen dissociation, a necessary input to computational fluid dynamics, also behaves similarly for all collision partners and strongly depends on the degree of thermal nonequilibrium. Using data for nitrogen dissociation and oxygen dissociation with partner N₂, the effect of each reactant state on dissociation is quantified. The effect of the collision partner’s internal energy on simple dissociation is found to be small and likely negligible. Finally, the effect of vibrational energy on simple dissociation is found to be stronger than the effect of rotational energy. These rigorous statistical analyses enable the development of physics-based models for computational fluid dynamics.