The Arc Spectrum of Europium.

Abstract

Most of the strong lines of Eu i arise from transitions between terms of multiplicity 10, 8, and 6, obtained by adding two electrons to (4f)7 8S0 of Eu Ill. This part of the spectrum is regular in every respect and contains typical multiplets and numerous short series. The lowest level is f7s2 8So. All the terms arising from the added electrons 6s7s, 6s8s, 6s5d, 6s6d, 6s6p, 6s7p, and 5d6p have been identified, and some from 6s7d, 6s5f, 6s6f, (5d)2, and (6p)2. There are many additional energy-levels, which probably arise from the configurations f6ds2 and f6d2s. The number of classified lines is i 156, including all but one of the 200 strongest. The ionization potential is 5.64 volis. Tables are given showing the terms and unclassified levels, the electron configurations, the sei~ies relations, the intensities in multiplets, and a complete list of classified lines. The probable error of a tabular wave length is ± 0.010 A for the stronger lines and ± 0.017 for the faintest group