First Spark Spectrum of Neodymium—Preliminary Classification and Zeeman Effect Data

Classification by means of the combination principle of 367 lines of Nd II as arising from 30 lower and 57 upper levels has been checked by Zeeman effect measurements at fields up to 87,180 oersteds, and by other data from the M.I.T.-W.P.A. wave-length project. Quantum numbers have been assigned to those levels which have approximate $\mathrm{LS}$ coupling, and $g$ values of all known levels have been determined. The lowest term is $4f^4\left({}_{}{}^5{}_{}{}^{}I\right)6s-a{}_{}{}^6{}_{}{}^{}I$. All of the low terms found arise from $4f^{4}6s$ and $4f^{4}5d$, while all identified upper terms are believed to arise from $4f^{4}6p$. The strongest lines in the spectrum belong to the sextet and quartet supermultiplets arising from the transition $4f^4\left({}_{}{}^5{}_{}{}^{}I\right)6p-6s$, but these show perturbations which give rise to important intensity anomalies which affect the selection of raies ultimes. Curves are given which show the variation, in the progression La II, Ce II, Pr II, and Nd II, of the binding of terms arising from the configurations $f^{n}s$, $f^{n}p$, $f^{n}d$ and, where known, $f^{n+1\mathrm{}}$.