The Vector Coupling in the Nickel-, Palladium-, and Platinum-Like Spectra

Spectroscopic data.---The 5d⁹6s and 5d⁹6p configurations are identified among the known levels of Pt I, and partly identified in Tl IV and Pb V. The lines observed in the condensed spark discharge of thallium λ868 to λ1070 and lead λ477 to λ1280 are listed.Vector coupling.---The relative energies, line intensities, and g-values of the levels of the d⁹s and d⁹p configurations of the sequences Ni I-Ge V, Pd I-Sn V, and Pt I-Pb V show a gradual transition from LS or Russell-Saunders coupling to jj coupling with increasing atomic number and increasing net charge. In the "pure" jj coupling the levels are arranged in groups (two in d⁹s and four in d⁹p). The positions of the d⁹p groups observed for Hg III, Tl IV, and Pb V agree well quantitatively with the positions independently calculated for jj coupling with the aid of the Sommerfeld regular doublet law. In the d⁹p configuration of Tl IV and Pb V, only levels built upon d⁹²D5/2 are observed in spite of the fact that the d⁹3/2+p1/2 levels are more stable than the d⁹5/2+p3/2 levels.Correlation of levels, with varying principal quantum number and varying nuclear charge.---In several cases among the spectra under consideration, levels of the same J-value cross when relative energy in a configuration is plotted against nuclear charge in an isoelectronic sequence. These levels, except in one case, happened to be recognizable on both sides of the "crossings" on account of their approximately normal intensities. But in general, correlation of levels and crossing or non-crossing in spectral series or isoelectronic sequences appears to be without meaning, for it necessitates considering quantum numbers or nuclear charges as continuous variables.