Reevaluation of the O+(²P) reaction rate coefficients derived from Atmosphere Explorer C observations

Abstract

O+(²P) is an important species for studies of the ionosphere and thermosphere: its emission at 7320 Å can be used as a diagnostic of the thermospheric atomic oxygen density. Unfortunately, there are no laboratory measurements of the O and N2 reaction rates which are needed to determine the major sinks of O+(2P). The reaction rates that are generally used were determined from aeronomic data by Rusch et al. (1977) but there is evidence that several important inputs that they used should be changed. We have recalculated the O and N2 reaction rates for O+(2P) using recent improvements in the solar EUV flux, cross sections, and photoelectron fluxes. For the standard solar EUV flux, the new N2 reaction rate of 3.4 ± 1.5 × 10−10 cm3 s−1 is close to the value obtained by Rusch et al. (1977), but the new O reaction rate of 4.0±1.9 × 10−10 cm3s−1 is about 8 times larger. These new reaction rates are derived using neutral densities, electron density, and solar EUV fluxes measured by Atmosphere Explorer C in 1974 during solar minimum. The new theoretical emission rates are in good agreement with the data for the two orbits studied by Rusch et al. and they are in reasonable agreement with data from five additional orbits that are used in this study. We have also examined the effect of uncertainties in the solar EUV flux on the derived reaction rates and found that 15 % uncertainties in the solar flux could cause additional uncertainties of up to a factor of 1.5 in the O quenching rate.