Daytime ion chemistry of N₂⁺

Rocket measurements of the emission of the (0, 0) first negative band of N2+ at 3914 A in the day airglow have been made between 120 and 300 km. The solar zenith angle at the time of the flight was 60°, and the zenith intensity above 120 km was 1.6 kR averaged over both legs of the flight. The data are compared with a model in which charge exchange of N2 with metastable O+(²D) ions is included as an additional source of N2 ionization. Above 240 km this mechanism is dominant over the photoionization of N2 by solar extreme ultraviolet radiation. The derived N2+ density is consistent with the results of rocket-borne mass spectrometric observations. About 600 Rayleighs of the observed 3914 A emission above 120 km is due to direct photoionization into the B²Σu+ state; the remainder results from resonance scattering of solar radiation by N2+.