The Intensity Distribution in the Nitrogen Band Systems Emitted from the Earth's Upper Atmosphere
Proceedings of the Royal Society A
The intensity distributions in the negative and first and second positive band systems of nitrogen are determined for a number of excitation mechanisms. The results are compared with the intensity distributions observed from upper atmospheric sources with a view to understanding the processes occurring. Ordinary aurorae are discussed in detail. It is shown that if the emission is attributed to electron excitation (as is commonly done) then it is necessary to assume that the vibrational
... ibrational temperature of the molecules is many thousands of degrees absolute-as similar views have been expressed by earlier writers on evidence that is now discredited it may be mentioned that in the present paper proper account is taken of the Frank-Condon principle. A more plausible interpretation of the observational results is that the heavy particles, that are often considered to form part of incident auroral streams, contribute to the excitation. High and low latitude aurorae show striking differences. The emission of the negative band system from sunlit aurorae and from the twilight sky is studied. The direct action of the solar radiation on nitrogen ions is responsible. In the case of sunlit aurorae the continued absorption and emission of the resonance bands raises the vibrational temperature of the ions: this greatly influences the intensity distribution. The consequences of the identification of the strong infra-red emission from the nocturnal sky with the (0, 0) band of the first positive system is discussed. It would appear that the identification necessitates a high degree of dissociation of the upper atmospheric nitrogen. Confirmatory observational work is urged. In the appendix a preliminary investigation on the energy distribution of electrons in aurorae is attempted. [ 217 ] 15-a * The higher vibrational levels were not treated as for these, the simple approximations used becomes less satisfactory. /S'-funci * The wave-length measurement is not precise as the dispersion of the spectrograph used was very low. t The presence of a few bands additional to those in. the table has been suggested. Thus the (7,8) and (9!, 7) bands have been identified with weak emissions a t A 3484 and A 3169 respectively. The proposals are not a t all plausible and will be ignored. X From the d ata in the two systems a crude (intensity correction)-(wave-length) curve ca<n be derived but the scatter is too great to make it of much value. * Cf. 'The model ionosphere' table published by Bates & Massey (1946) . These authors also give reasons for supposing th at the recombination proceeds by an electronic, not ionic, reaction. t If may well be greater: if this is the case A becomes smaller. Intensity distribution in the nitrogen band systems Vol. 196. A.