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g), ION-PAIR STATES, AND OXYGEN ATOM RECOMBINATION.
D. L. HUESTIS, C. G. BRESSLER AND R. A. COPELAND, Molecular Physics Laboratory, SRI International, Menlo Park, CA 94025.
\par Collisions of oxygen or nitrogen molecules with laser-excitated high vibrational levels of O2(A3
u+) 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 5g valence state of O2. The regular sequence of vibrational bands observed suggests that the upper state is an ion-pair state of O2, 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. \par
Ab initio calculations [2,3] indicate that, although quite weakly bound, at large internuclear distances the 5g 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 O2 and implications for oxygen atom recombination and the role of O2(5g) in predicting atmospheric nightglow emissions [6]. \par
\setlength\parskip0mm \noindent References:
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[1] C. G. Bressler and R. A. Copeland, ``Collisional Production and Removal of O2 in the 5g State,'' in preparation. \par \hi
[2] R. P. Saxon and B. Liu, J. Chem. Phys. 67, 5432 (1977). \par \hi
[3] H. Partridge, C. W. Bauschlicher, S. R. Langhoff, and P. R. Taylor, J. Chem. Phys. 95, 8292 (1991). \par \hi
[4] P. C. Wraight, Planet. Space Sci. 30, 251 (1982). \par \hi
[5] D. R. Bates, Planet. Space Sci. 36, 875 (1988). \par \hi
% first reference on the blank line below [6] T. G. Slanger and D. L. Huestis, J. Geophys. Res. 86, 3551 (1981). \par
\noindent Acknowledgments:
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This work is supported by the NASA Sun-Earth Connection and Planetary Atmospheres Programs.