The spectra of doubly- and trebly-ionised phosphorus (P III and P IV)

Abstract

Previous to the classification of some of the lines of the phosphorus spectrum into series of the doubly-ionised atom, which is described in the present paper, no series had been observed for the elements of group V of the periodic table. The element phosphorus of this group was selected for investigation because the spectrum corresponding to each stage of ionisation was expected to bear a marked resemblance to that of the silicon atom of one lower stage of ionisation, of the aluminium atom of two stages lower, of the magnesium atom of three stages lower, and so on. The series corresponding to successive stages of ionisation of some of these atoms had already been worked out, and hence, if the series spectra of phosphorus could be observed, a direct comparison would be possible. The spectrum of the neutral atom of phosphorus has been identified and described by the present writer, but no series relationships have been found. This is probably due to the limited range of the spectrum which it has been possible to investigate so far. The region investigated by Geuter in 1907 extends from λ 5727·90 to λ 2389·93 and contains 530 lines which are ascribed to phosphorus. Kayser gives also the approximate wave-lengths of a few more lines at the red end up to λ 6505. Only four of these lines belong to the arc spectrum, and the rest are therefore lines of phosphorus at one or more stages of ionisation.