Investigations on the spectrum of selenium. IV.─Se I and Se VII

In the course of these investigations, which are mainly directed towards a study of the characteristic energy levels of the spark spectra of selenium, several lines have been obtained, which from experimental evidence, could be assigned definitely to the arc spectrum of the element. for the complete excitation of the arc spectrum, recourse must be had to special methods such as the addition of a foreign gas used by Rungs and Paschen, or an electrodeless discharge in the manner adopted by Gibbs and Ruedy. The sources in our investigations were chiefly discharges through narrow capillary tubes with varying amounts of inductance and capacity, vacuum sparks and a vacuum arc with selenium tipped graphite or aluminium electrodes. It has been found that many are lines are excited even in the ordinary uncondensed discharge and in the vacuum arc. However, the arc in an atmosphere of nitrogen in the manner adopted previously for Si, Ge, As has been specially used to isolate, in the fluorite region, the lines belonging to the neutral atom. The data presented in this Part have been based on measurements of plates taken with all these sources. In the arc spectrum of selenium, Rungs and Paschen discovered a sharp and a diffuse series systems of what were then considered to be triplets. Later, McLennan, McLay and McLeod brought these quintet groups into consonance with the predictions from Hund's theory, and by studying the arcin vacuo in the fluorite region, identified combinations involving the low-lying triplet levels. Recently, Gibbs and Ruedy have detected a few more combinations, in particular the member 5s 5 S—5p 5 P in the extreme red which has enabled them to establish a connected system of term values. With the aid of the observations made by us it has been possible to assign about 50 lines between λ 3619-λ 1414 to the neutral atom of Se, and to detect among these a number of new energy levels of Se I.