Examination of Water Dissociation Models in Shock Heated Air

Abstract

A semiclassical molecular dynamics approach is used to model the dissociation of water to form the hydroxyl radical. The unimolecular dissociation of water is utilized to compute the probability of reaction, as well as to determinetheproductOHtranslational,vibrational,androtationalenergydistributions.Thee owregimeofinterest is that between 80 and 100 km, so that a raree ed gasdynamics technique must be used. The molecular dynamics probabilities of reactions and product distributions are, therefore, used in the direct simulation Monte Carlo method to model spatial distribution and temperatures of OH in the bow shock of a 5-km/s vehicle. The fraction of translational energy transferred to internal water energy during dissociative collisions was parameterized. The rates of OH production predicted by the molecular dynamics model are approximately a factor of e ve lower than those predicted by the total collisional energy model for 10% energy transfer and are approximately equal for 100% energy transfer.