A post-collision internal energy model for O(3P) + SO2([formula omitted][formula omitted]) in DSMC based on Molecular Dynamics computations

Abstract

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.