Herzberg Oxygen Bands in ``Air'' Afterglows and the Night Airglow

Abstract

The ultraviolet A³Σ_u⁺—X³Σ _g^— oxygen bands have been observed in emission from greenish‐white ``air'' afterglows containing 95–98% nitrogen and 2% to 5% oxygen. The afterglows were excited by an electrodeless rf oscillator and examined with a grating spectrograph having an f/2 camera and a dispersion of 30 A/mm. The mechanism of excitation of these bands in the afterglow may be either the reaction N+O₃→NO+O₂ or the reaction N+NO₂→N₂+O₂. A comparison of the afterglow spectrogram with an ultraviolet night airglow spectrogram shows that bands arising from higher vibrational levels are more intense in the airglow than in the afterglow. Collisional de‐excitation can account for the lower vibrational temperature in the laboratory. The atomic nitrogen‐ozone reaction also may occur in the chemosphere between 60 and 90 km and may contribute to the excitation of the night airglow Herzberg bands. The atomic nitrogen at this level could come from daylight predissociation of NO and N₂ and from the twilight dissociative recombination of ionized NO.