Development of a chemistry model for vibronically excited species in direct simulation Monte Carlo

This article presents the derivation of a five-species air mixture chemistry model that accounts for the electronic excitation of all species. The chemistry model consists of a vibronic extension of the quantum-kinetic (QK) chemistry models for the direct simulation Monte Carlo (DSMC) method. Grounded on first-principle calculations and benefiting from the development of the vibronic model in DSMC, the vibronic QK model provides an electronic state-specific description of kinetic processes. The vibronic QK model is validated against the most representative experimental measurements and quasi-classical trajectory calculations for the 19 chemical reactions constitutive of the five-species air model in both thermal equilibrium and non-equilibrium. The vibronic QK model demonstrates excellent reproduction of the reference database in both thermal equilibrium and non-equilibrium. The vibronic QK model presents slower reaction rates than the former QK model, especially for the dissociation of nitric oxide. Additionally, the model is verified for the decomposition of an air mixture in typical post-shock flow conditions. It is shown that the vibronic QK model accurately recovers the detailed balance principle and achieves appropriate thermochemical equilibrium. Finally, the model is applied to canonical hypersonic flows past a cylinder body, demonstrating the inaccuracy of the traditional assumption of the electronically excited states being distributed according to the Boltzmann statistics. It is also shown that the population of the electronically excited states and their vibrational quantum levels strongly deviate between the two approaches, suggesting a significant impact on the line intensity of the molecular species' absorption spectrum.