Investigations on the spectrum of selenium. Part I.—Se IV and Se V

In continuation of the previous work on germanium and arsenic by one of the writers (K. R. R.), an extensive investigation of the spectrum of selenium has been undertaken in order to analyse the spectra of the atom at successive stages of ionisation and determine the energy levels characteristic of each. In the present part an account is given of the general experimental methods adopted in these investigations and the results obtained for the spectra of Se IV and Se V. The other spectra of the element, a consideration of which is in progress, will form the subject of succeeding parts. Of the earlier measurements of the spark spectrum of selenium, those by Messerschmidt are extensive and range from λ 5898 to λ 2340. McLennan and Young have recorded 12 lines in the spark and 5 lines in the arc between λ 2200 and λ 1850. McLennan, Young and Ireton have also measured the vacuum arc spectrum in the region λ 2296 to λ 1492. However, in the Schumann region extending to λ 1230, the measurements by Lacroute are more complete. Bloch and Bloch have investigated, on two occasions, the spectrum of an electrodeless discharge through selenium vapour by varying the length of the auxiliary gap in series with the discharge and have assigned all the lines of selenium between λ 6783 and λ 2196 to the different stages Se I, Se II, Se III and Se IV.