Characterization of vibrational and rotational energy transfer in N₂ + N₂ dissociative collisions using the quasiclassical trajectory method

Dissociation of diatomic molecules is an important chemical process in high-temperature hypersonic ows. Here, we highlight key findings from a study of nitrogen dissociation via N₂ + N₂ collisions using the quasiclassical trajectory (QCT) method. The study is comprehensively documented in a companion paper.¹ Over 2.4 billion trajectories were computed at a range of translational-rotational and vibrational temperatures. The simulations used an improved potential energy surface for the N₄ system. Thermal equilibrium and nonequilibrium dissociation rate constants are reported. The Park two-temperature model's predictions for these rate constants are smaller than the QCT values in almost all cases, and the discrepancy is largest at strongly nonequilibrium conditions. "Swap" disso- ciation processes and quasibound reactant states are significant, and their contributions to the dissociation rate constant are quantified. The effect of dissociation on vibrational and rotational energy transfer is discussed, with several key conclusions. (1) At thermal equilibrium, dissociation tends to result in a large vibrational energy loss and a small rotational energy loss from the N4 system. (2) At nonequilibrium, when T_v falls below T = T_t = T_r, rotational energy losses increase and the role of vibrational energy in promoting dissocia- tion lessens. (3) At both thermal equilibrium and nonequilibrium, dissociating trajectories consistently result in an average total internal energy loss of about 10 – 11 eV.