The spectra of trebly-ionised oxygen (O IV) and trebly-ionised nitrogen (N IV)

Abstract

The spectrum of trebly-ionised oxygen has been investigated in the extreme ultra-violet by Bowen, who has identified five of the deepest doublet terms, namely 2 p 2 P, 2 p' 2 S, 2 p' 2 P, 2 p' 2 D and 2 p 3 2 P. A list of 76 lines in the near ultra-violet, attributed to O IV, was given by Mihul, but no classifications were made. The present paper deals mainly with the identification of the 3 s 2 S, 3 p 2 P, 3 d 2 D terms of the doublet system, and of the 3 s' , 3 p' and 3 d' terms of the quartet system from their combinations occurring in the visible and near ultra-violet regions. The spectrum has been photographed on various instru­ments from λ 7000 to λ 1250 by using strongly condensed discharges in vacuum tubes containing oxygen. The detection of some of the fainter multiplets was greatly facilitated by the prediction of their positions by extrapolation from corresponding multiplets in C II and N III. As the region investigated is rich in lines of O II and O III, there are many instances of O IV lines being masked by lines of O II and O III.