All the previously unknown $5d^{10}$, $5d^{9}6s$ and $5d^{9}6p$ levels in all the stable members of the platinum-like isoelectronic sequence, and some $5d^{9}6d$ and $5d^{9}7s$ levels, have been identified. Several corrections are made to the literature on Au II, Hg III and Tl IV. The Pb V and Bi VI classifications verify Arvidsson's estimates of the stages of ionization for the individual lines. The $5d^{9}6p{|}_0$ levels were found only in consequence of Goble's predictions from his solution of the four-vector problem. The dependence of the energy and intensity values upon the atomic number is very smooth, except for a branching effect explained by Goble. New $d^{9}s$ screening numbers and Houston parameters are given. Ionization potentials are estimated, by a comparison method, up to 87.9±0.7 volts for Bi VI. Analysis of the one (partly resolved) hyperfine structure pattern attributed to Bi VI yields a splitting factor $a\left(6s\right)=3.1\mathrm{}\pm 0.2$ ${\mathrm{cm}}^{-1\mathrm{}}$.

• Received 24 April 1935

DOI:https://doi.org/10.1103/PhysRev.48.357