Effect of O₂ + O ab initio and Morse additive pairwise potentials on dissociation and relaxation rates for nonequilibrium flow calculations

This work quantifies the sensitivity of O₂ + O dissociation rates and relaxation to interatomic potential energy surfaces at high-enthalpy, nonequilibrium flow conditions. State-to-state cross sections are obtained by quasi-classical trajectory (QCT) calculations with two potential surfaces. The first is a Morse additive pairwise potential for O₃ that is constructed based on $O 2 ( 3 Σ g − )$ spectroscopic measurements and the second is a double many-body expansion potential by Varandas and Pais [Mol. Phys. 65, 843–860 (1988)]. The QCT calculations of cross sections and rates with the two surfaces are compared to each other and shock tube measurements. It is found that, at temperatures between 2500 K and 20 000 K, the equilibrium dissociation rates predicted by the two potentials agree within 12%, and they are bound by experimental dissociation measurements. In contrast, above 10 000 K, ab initio based equilibrium dissociation rates are about a factor of two higher than the widely used Park’s model. The nonequilibrium dissociation rates calculated by the two potentials are within 70% while phenomenological models differ by two orders of magnitude for vibrationally cold conditions of shocks. The analyses provide an approach for improving accuracy of nonequilibrium high-enthalpy flow modeling when ab initio potentials are not available.