Reevaluation of Charge Exchange Cross Sections Related to Energetic Neutral Atom Detection in the Magnetosphere Rainer A. Dressler and Edmond Murad Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, MA 01731 Thomas M. Stephen and Bert Van Zyl Department of Physics and Astronomy, University of Denver, 2112 E. Wesley Ave., Denver, Colorado 80208 Energetic neutral atoms (ENAÕs) produced in charge-exchange collisions between magnetospheric ions and exospheric neutrals present a means to image remotely the plasma-dynamics of the magnetosphere. ENA detectors play a central role in the Imager for the Magnetopause-to-Aurora Global Exploration (IMAGE) satellite mission. The interpretation and quantification of observed ENA signals depend upon the knowledge of the energy dependence and magnitude of the appropriate charge exchange cross sections. A review of existing experimental cross sections for H+ and O+ impacting H, O, O2 and N2 is presented. In addition, theoretical studies for the H+ + H, O+ + H, H+ + O and O+ + O charge-exchange pairs are reviewed. As a proto-typical case, the non-symmetric (O + H)+ pair, for which significant discrepancies exist in the literature, is examined in detail. Classical and semi-classical differential cross section calculations are compared with existing measurements. New semi-classical calculations of the integral cross sections for this case are presented. The calculations are based on high-level ab initio OH+ interaction potentials and exchange energies (1), and use resonant charge exchange theory (2) including angular momentum conservation constraints. This approach is justified for the non-symmetric system at the energy range of interest given the accidental resonance in the (O + H)+ system. 1. G. Chambaud, J. M. Launay, B. Levy, P. Millie, E. Roueff and F. Tran Minh, J. Phys. B 13, 4205 (1980). 2. H. S. W. Massey and H. B. Gilbody, Electronic and Ionic Impact Phenomena, 2 ed. (Oxford University Press, London, 1974). _______________ Presented at the Fall American Geophysical Union Meeting, San Francisco, CA., December 15-19, 2000