On the development of a new nonequilibrium chemistry model for mars entry

This paper represents a summary of results to date of an on-going effort at NASA Ames Research Center to develop a physics-based non-equilibrium model for hypersonic entry into the Martian atmosphere. Our approach for the determination of reaction rate coefficients is to first compute potential energy surfaces based on accurate solutions of the electronic Schrödinger equation and then use quasiclassical trajectory calculations to obtain reaction cross sections and rate coefficients based on these potentials. We have presented new rate coefficients for N₂ dissociation and CO dissociation and exchange reactions. These results illustrate shortcomings with some of the rate coefficients in Park’s original T-T_v model for Mars entries and with some of the 30-45 year old shock tube data. We observe that the shock tube experiments of CO + O dissociation did not adequately account for the exchange reaction that leads to formation of C + O₂. This reaction is actually the primary channel for CO removal in the shock layer at temperatures below 10,000 K, because the reaction enthalpy for exchange is considerably lower than the comparable value for dissociation. The rate coefficients reported herein should reduce the uncertainty in modeling hypersonic flows expected for entry of heavy spacecraft into the Martian atmosphere.