Quantum-kinetic chemistry model with an anharmonic oscillator model: Model derivation and limitations

This work presents a new formulation of the quantum-kinetic (QK) chemistry models, in which the vibrational excitation is modeled with an anharmonic oscillator model. The new formulations are applied to some of the most representative dissociation reactions occurring during an Earth re-entry. The newly derived analytical expressions are implemented in a direct simulation Monte Carlo (DSMC) solver. The DSMC reaction rates demonstrate excellent agreement with the newly derived analytical expressions, verifying the successful implementation in the DSMC solver. The new models suggest that dissociation reactions are more likely to occur than with the original QK models. Furthermore, the new formulations are compared against experimental measurements, high-fidelity calculations, and well-established chemistry models for both thermal equilibrium and non-equilibrium conditions, presenting reasonable agreement with the baseline database. Additionally, the limitations of the new formulations are assessed for thermal non-equilibrium conditions where an excessive utilization of the relative translational energy and insufficient utilization of the pre-collision vibrational energy to promote dissociation reactions is found.