State-to-state dissociation and recombination modeling in DSMC using quasi-classical trajectory calculations for O + O₂

A state-based approach is used to model dissociation and recombination reactions for O + O₂ collisions using cross-section data from quasi-classical trajectory (QCT) calculations. The dissociation cross section data are fit to a functional form and interpolated for implementation in a DSMC (direct simulation Monte Carlo) solver. The QCT dissociation probabilities are expressed in terms of these cross sections. A two-step binary collision (TSBC) model employing detailed balance and microscopic reversibility is used to characterize the recombination probabilities in terms of the dissociation cross sections. The QCT database used in this work is rotationally-averaged, and as such will mainly assess the effect of the vibrational mode on dissociation and recombination. The performance of state-based dissociation and recombination models is assessed through comparisons to two phenomenological DSMC models: the total collision energy (TCE) model and the quantum-kinetic (QK) model. Comparisons are made using the following quantities: equilibrium total dissociation and recombination rates, equilibrium state-specific dissociation and recombination rates, nonequilibrium total dissociation rates. The evolution of temperatures, state distributions and number densities are also compared through a non-equilibrium isothermal heating case.