Relative population of OH X 2Π levels

Abstract

Intensities of nightglow bands in the visible and the near infra-red region of the OH rotation vibration system are presented. Comparison with other similar measurements shows a fair consistency, and the absolute intensities given do not, except in a couple of cases, deviate seriously from those predicted previously. The relative population of the vibrational levels υ = 3 to 9 of the OH ground state is computed from the intensities by means of relative transition probabilities given by some previous investigators. The values obtained are, in descending order, from υ = 9:1·0, 1·25, 1·9, 2·6, 5·1, 7·0 and (8·1). The transition probabilities given by one investigator give somewhat larger values. Relative excitation numbers of the different levels have been evaluated from the relative population. It is concluded that excitation of the vibrational levels of the OH ground state takes place at all levels and that the relative number of molecules excited at different levels is about the same. The bearing of these results on the theories of Bates, Nicolet and Herzberg and of Krasovskii is discussed.