The Spark Spectrum of Europium, Eu II

Abstract

Structure of the spectrum. The strongest lines of Eu II arise from transitions based on the ground-level of Eu III, ${f}^{7}^{8}S^{\mathrm{o}}$. The lowest terms are ${f}^{7}s^{9}S^{\mathrm{o}}$, $^{7}S^{\mathrm{o}}$. Next come ${f}^{7}d^{9}D^{\mathrm{o}}$, $^{7}D^{\mathrm{o}}$. Numerous levels, combining with these terms, arise from ${f}^{6}{s}^{2}$, ${f}^{6}\mathrm{sd}$, and ${f}^{8}$. The number of levels identified is 156; of lines classified, 467. All the stronger lines are included. Unclassified lines. About 2000 lines remain unclassified. They probably arise from transitions between levels based upon higher limits in the ${f}^{7}$ configuration of Eu III. Ionization potential. Series of three consecutive $^{9}S^{\mathrm{o}}$ and $^{7}S^{\mathrm{o}}$ terms give the value 11.21 volts. Zeeman effect. Patterns for 459 lines, measured at the Massachusetts Institute of Technology, with a field of 87,850 gauss, are tabulated. The $g$ values for 118 levels have been determined. Those for the low levels agree with theory; the higher levels are much perturbed. Patterns for a few lines of Eu I and Eu III are given. The latter confirm that the ground state is $^{8}S^{\mathrm{o}}$.