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

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.