Modeling of OH vibrational distributions using molecular dynamics with the direct simulation Monte Carlo method

A semi-classical molecular dynamics approach is used to model the dissociation of water to form the hydroxyl radical. The unimolecular dissociation of water is used to model the probability of reaction as well as determine the product OH translational, vibrational, and rotational energy distributions. The altitudes of interest are between 80 to 100 km, so that a rarefied gas dynamics technique must be used. The molecular dynamics probabilities of reactions and product distributions will be used in the direct simulation Monte Carlo method to model spatial distribution and temperatures of OH in the bow-shock of a 5 km/sec vehicle. Ultraviolet spectra of the OH(X → A) transition will be modeled and compared with data from the Bow Shock Ultraviolet Flight Experiment 2. The flow and spectral modeling shows that the use of fundamental water dis-sociation probabilities and product distributions is crucial in predicting the OH vibronic spectra. Excellent agreement of the spectral features between theory and experiment is obtained.