Metastable Atoms and the Auroral Afterglow of Nitrogen

The auroral afterglow of nitrogen is attributed to N atoms in the high metastable level 6S which in binary collisions with normal N atoms produce excited N2+ ions and with normal N2 molecules excite their spectrum. This hypothesis explains (1) the high energy of the levels emitting light, (2) the dominant instantaneous intensity of the brief duration auroral afterglow, (3) the absence of the N2+ bands in Kaplan's ``blue afterglow,'' and (4) the suppression of the same bands by oxygen impurity.