Analysis of Associative Ionization Rates for Hypersonic Flows

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Analysis of Associative Ionization Rates for Hypersonic Flows

Boyd, Iain D. / Josyula, Eswar

Three of the key associative ionization reactions that lead to plasma formation around hypersonic vehicles are studied in detail. For production of ${NO}^{+}$ , $O_{2}^{+}$ , and ${CO}^{+}$ , cross sections derived from experimental measurements for the interactions of atoms in low-lying electronic states are compared to cross sections derived from the overall rates widely used to model these processes. The experimentally derived cross sections are then used to develop rate coefficients for each of the atomic interactions, including those in electronically excited states. Monte Carlo simulation is employed to determine the postreaction partitioning of energy across the products. The key finding of this study is that associative ionization for all three systems proceeds primarily through interactions involving at least one of the atoms lying in the first or second electronically excited state. Nonequilibrium between the translational and electronic modes of the atoms will therefore lead to a variation in the associative ionization rates. This conclusion indicates a need for a more comprehensive approach to modeling plasma generation in hypersonic flows that resolves the lowest lying electronic states of the atoms that participate in associative ionization.