Photochemistry of N₂⁺ in the daytime F region

The photochemistry of N 2 + in the daytime F region continues to be a source of concern due primarily to the uncertain roles of the metastable O + (²D) ion and possible vibrational excitation. This investigation adopts a unique subset of data from the Atmosphere Explorer C satellite that spans distinct regions near the low‐latitude F peak wherein either chemical reactions or electron processes alternatively control the N 2 + abundances. Concentrations of N 2 + calculated according to current theory and including recent laboratory data for O + (²D) losses via N 2 are found to exceed ionospheric observations between 220 and 400 km by a factor near 2. Relevant characteristics of the basic molecular ion concentration measurements are described, along with an analysis for select orbits conducted according to current photochemical equilibrium theory. Possible simple modifications of this theory are discussed in terms of the constraints suggested by the nature of the observations.