The Second Spectrum of Ytterbium (Yb II)

The analysis of Yb II provides the most complete interpretation of a complex rare-earth spectrum known to date. The total number of energy levels is 315; 141 even levels and 174 odd levels. Three coupling schemes are represented: LS-coupling for the terms 4f ¹⁴ ns ²S(n = 6, 7, 8); 4f ¹⁴ nd ²D(n = 5, 6, 7) and 4f ¹³ 6s ^{2 2}F°: J _I J _II-coupling for the levels from the configurations 4f ¹³ 6s 6p and 4f ¹³ 5d 6p; and J _I L _II-coupling for those from the 4f ¹³ 5d 6s and 4f ¹³ 5d ² configurations. More than 5000 Yb II lines are listed, of which about 80 percent have been classified, and 95 percent of the total intensity is accounted for. Observed Zeeman patterns for over 1000 lines have yielded g-values for 258 levels. The agreement between observation and theory is excellent as regards both the positions of the energy levels and the g-values. The theoretical work was done in collaboration with Racah and his associates over more than a decade. A limit, 98150 K, giving an ionization potential of 12.17 eV, has been derived from the three-member ²S series.