Arc spectra of gallium, indium, and thallium

Abstract

The arc spectra of gallium, indium, and thallium have been systematically investigated photographically in the octave 6500 to 13000 Angstroms. The spectra were excited in direct-current arcs and recorded on infrared sensitive photographic emulsions with a concave diffraction grating 22 feet in radius. In the designated spectral range, 37 new lines were photographed in Ga i, 35 lines in In i, and 25 lines in Tl i. All the observed lines are explained as combinations of doublet terms arising from the axial and orbital momenta of a singlevalence electron. The new data led to a revision of Ga i terms, and extension from n = 9 to 12 for ns S, from n = 7 to 11 for nd D, and to the discovery of n/F° terms from n = 4 to 7. Besides confirming many terms already known for In i and Tl i, two new nf F° terms were found for each of these spectra.