Excitation processes in the night sky and the aurora
It is shown that the main features in the selective emission spectra of the night sky and the aurora, namely, the forbidden [OI] lines, the various systems of bands of N2+ and N2 and O2, and in particular, the enhancement of certain lines and bands relative to others and the diurnal variations of the intensity of certain lines in the night sky, can be satisfactorily explained on the view that all the excitation and quenching processes in the upper atmosphere are collisions of the second kind, of the resonance type, between the metastable atoms and molecules of nitrogen and oxygen. The metastable atoms are generated in the night by collisions between the metastable molecules; the latter are in turn formed by the recombinations of the normal atoms which are produced by photo-dissociation of the molecules during the day. A strong argument for the theory is that, not only the observed radiations are provided with reasonable excitation processes, but the absence of other atomic lines N, O, H and the rare gases is automatically accounted for by maximum energy available for the excitations in these metastables, which is only 6·1 volts (the energy of N2 [A3Σ]). It is suggested that these processes in Table II are the microscopic processes responsible for the observed spectra, while such large-scale features as the shapes of the aurorae and seasonal variations in the intensities, etc., may have to be explained by further hypotheses.
Ta-You Wu1 2