Analysis of Chemistry Models for DSMC Simulations of the Atmosphere of Io

Abstract

Hypervelocity chemical reactions between SO2 and O are studied using the molecular dynamic/quasi-classicaltrajectory method for conditions relevant to the modeling of the rarefied atmosphere of Io, a moon of Jupiter. The implementation of both molecular dynamic/quasi-classical-trajectory and total-collisional-energy chemistry reactionmodelsindirectsimulationMonteCarloisstudiedinazero-dimensionaltime-dependentanalysisandatwodimensionalaxisymmetricdirectsimulationMonteCarlosimulationtomodelasimpleplanetary flowcondition.The molecular dynamic/quasi-classical-trajectory simulations were found to result in lower reaction rate constants and reactionprobabilitiesthanthetotal-collisional-energymodel,andthevibrationalfavoringfeatureoftheSO2 � O ! SO � 2O reaction was revealed. The total collision cross section using the more general viscosity cross section was also obtained through the molecular dynamic/quasi-classical-trajectory simulations and was found to have a significantlydifferentenergydependencecomparedwiththeoriginalvariablehardspherecrosssection.Forthetwodimensional direct simulation Monte Carlo simulations it was found that the structure of the flow as well as the chemically formed sulfur oxide were different for the molecular dynamic/quasi-classical-trajectory and the totalcollisional-energy reaction probabilities and total cross sections. In addition, the reaction region was found to be highly nonequilibrium, which suggests that molecular dynamic/quasi-classical trajectory is a more suitable chemistry model for the simulation of Io’s atmosphere.