A post-collision internal energy model for O(3P) + SO2(X,1A1) in DSMC based on Molecular Dynamics computations

•SO2-O MD/QCT collisions computed for conditions relevant to the Ionian atmosphere.•Post-collision SO2 and post-reaction SO internal energy distributions determined.•Methodology for employing MD/QCT energy distributions in DSMC is presented.•DSMC thermal nonequilibrium heat bath cases computed to determine model's effect.•MD/QCT energy model affected time to equilibration, post-collisional temperatures.

A model is developed for determining molecular internal energies after O(3P) + SO2(X,1A1) collisions in the Direct Simulation Monte Carlo (DSMC) method in order to improve modeling of the hyperthermal interactions occurring in the upper atmosphere of Io. Molecular Dynamics/Quasi-Classical Trajectory (MD/QCT) studies are conducted to generate post-collision SO2 and post-dissociation SO internal energy distributions as a function of initial SO2 internal energy and relative collision velocity, which are found to be an improvement over the baseline Larsen-Borgnakke (LB) method that often predicts unphysical internal energies above the dissociation energy for non-reacting collisions and under-predicts post-dissociation SO internal energy. An approach for sampling from the MD/QCT-based internal energy distributions in DSMC is developed and DSMC simulations are then conducted for a time-dependent thermal nonequilibrium heat bath using both the MD/QCT-based distributions and the LB model. When only SO2-O collisions are considered, noticeable differences are observed for post-collisional SO2 and SO internal temperatures.

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