Doubly charged atomic oxygen ions in the thermosphere, 1. Photochemistry

Abstract

Measurements of O++ concentrations made by the Atmosphere Explorer C satellite are analyzed for altitudes where photochemical equilibrium conditions prevail in order to determine the photochemical sources and sinks of the doubly charged ion. The major loss process is found to be through partial charge exchange with neutral atomic oxygen with a rate coefficient of 1 × 10−11 cm³ s−1 with an uncertainty of 40%. Above 220 km the major source is photo-ionization of O+. However, X ray ionization of O(λ ≤ 23.3 Å) producing O++ directly through the Auger process provides a better fit to the observed profile at lower altitudes. At solar maximum, particularly during solar disturbances, this process could be a major source of ionospheric O++ up to 500 km.