Low-Energy Level Structure of Neutral Cerium (Ce I)

Abstract

The low portion of an extensive level structure derived from analysis of the optical spectrum is reported. Positions, $J$ values, and ${g}_{J}$ factors are given for 98 levels, including all 91 levels expected below 10 000 ${\mathrm{cm}}^{\ensuremath{-}1}$. A previous report on this analysis showed the ground level to be $4f5d6{s}^{2} ^{1}G_{4}^{\ensuremath{\circ}}$ and gave the lowest levels of $4f5{d}^{2}6s$. Comparison of the observed odd-parity levels with calculations by Goldschmidt and Salomon shows that all 86 of the odd levels tabulated here belong to these configurations. All but seven of these odd levels are assigned $\mathrm{LS}$ names, although the calculations show that many of them have low $\mathrm{LS}$ purities, and a few have strong mixtures of the two configurations. The much simpler system of even levels below 10 000 ${\mathrm{cm}}^{\ensuremath{-}1}$ includes only the six levels of $4{f}^{2}6{s}^{2} ^{3}H$ and $^{3}F$, beginning with $^{3}H_{4}$ at 4762.718 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the ground-state level. The table of even levels also includes $4{f}^{2}6{s}^{2} ^{1}G_{4}$ and the lowest two levels of each of the lowest two terms of $4{f}^{2}5d6s$, $^{5}I_{4,5}$, and $^{5}K_{5,6}$.