The Arc Spectrum of Selenium

Abstract

The arc spectrum of selenium, as excited by means of a positive column discharge in helium, has been photographed over the wave-length range 300-11,000A. Four different grating spectrographs were used having dispersions of from 11 to 2.5A per mm. A total of 510 lines has been measured as belonging to the arc spectrum and of these 391 have been classified. Seven series built on the ${}_{}{}^4{}_{}{}^{}S$ state of the ion have been carried to five or more members and the absolute term values are determined to within 0.2 ${\mathrm{cm}}^{-1\mathrm{}}$. All the $4p^4$, $4p^3\left({}_{}{}^2{}_{}{}^{}D\right)5s$, $4p^3\left({}_{}{}^2{}_{}{}^{}P\right)5s$, and $4p^3\left({}_{}{}^2{}_{}{}^{}D\right)5p$ terms have been located and also some of the $4p^3\left({}_{}{}^2{}_{}{}^{}D\right)4d$ terms. Perturbation effects are frequently evident and are illustrated by plots of the various series.