# $O_{2}(^{5}\Pi_{g})$, ION-PAIR STATES, AND OXYGEN ATOM RECOMBINATION

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 Title: $O_{2}(^{5}\Pi_{g})$, ION-PAIR STATES, AND OXYGEN ATOM RECOMBINATION Creators: Huestis, D. L.; Bressler, Christian G.; Copeland, Richard A. Issue Date: 1998 Publisher: Ohio State University Abstract: Collisions of oxygen or nitrogen molecules with laser-excitated high vibrational levels of $O_{2}$ produce a longer lived excited state, whose resonant multiphoton ionization (REMPI) spectrum cannot be assigned to any known singlet or triplet system [1]. We attribute the lower state of this new transition to the predicted [2,3] but previously unobserved ${^{5}}\Pi_{g}$ valence state of $O_{2}$. The regular sequence of vibrational bands observed suggests that the upper state is an ion-pair state of $O_{2}$, dissociating to $O^{+} + O^{-}$. Two vibrational levels have been observed in the lower state and ten in the upper state, the latter in the range 97,000 to $100,000 cm^{-1}$. Ab initio calculations [2,3] indicate that, although quite weakly bound, at large internuclear distances the ${^{5}}\Pi_{g}$ valence state should be the lowest of the states dissociating to ground state atoms. Because of its high degeneracy it could be a key intermediate state in $O + O$ recombination [4,5]. We are developing a more detailed and quantitative theoretical model of $O + O + M$ collisions. In addition to the experimental spectroscopy and kinetics results, we will also present preliminary work on spin-orbit resolved long-range potential curves for $O_{2}$ and implications for oxygen atom recombination and the role of $O_{2}(^{5}\Pi_{g})$ in predicting atmospheric nightglow emissions [6]. Description: References: [1] C.G. Bressler and R.A. Copeland, Collisional Production and Removal of $O_{2}$ in the ${^{5}}\Pi_{g}$ State,'' in preparation. [2] R.P. Saxon and B. Liu, J. Chem. Phys. 67, 5432 (1977). [3] H. Partridge, C.W. Bauschlicher, S.R. Langhoff, and P.R. Taylor, J. Chem. Phys. 95, 8292 (1991). [4] P.C. Wraight, Planet Space Sci. 30, 251 (1982). [5] D.R. Bates, Planet. Space Sci. 36, 875 (1988). [6] T.G. Slanger and D.l. Huestis, J. Geophys. Res. 86, 3551 (1981). Acknowledgments: This work is supported by the NASA Sun-Earth Connection and Planetary Atmospheres Programs. Author Institution: Molecular Physics Laboratory, SRI International URI: http://hdl.handle.net/1811/19009 Other Identifiers: 1998-TB-08