A Diagram of Some of the Energy Levels of Gadolinium IV in the Crystal Lattice as Obtained from the Ultraviolet Absorption Spectra of Gd${\mathrm{Cl}}_3$·6${\mathrm{H}}_2$O and Gd${\mathrm{Br}}_3$·6${\mathrm{H}}_2$O

A number of electronic energy levels of the gadolinium ion in the crystals Gd${\mathrm{Cl}}_3$·6${\mathrm{H}}_2$O and Gd${\mathrm{Br}}_3$·6${\mathrm{H}}_2$O were obtained from their ultraviolet absorption spectra. The intervals between these levels were found for the ion in Gd${\mathrm{Cl}}_3$·6${\mathrm{H}}_2$O and in Gd${\mathrm{Br}}_3$·6${\mathrm{H}}_2$O at room temperature and at that obtained with liquid air and in Gd${\mathrm{Cl}}_3$·6${\mathrm{H}}_2$O also at the temperature reached with liquid hydrogen. Levels were found to be decomposed by a magnetic field into doublets of enormous separations amounting to as much as 15 times the normal Larmor precession. Transitions occurred with large changes in magnetic moment which were different along the different axes of the crystal. The intervals between the electronic levels in the absence of a magnetic field are much smaller than might be expected for an ionic crystal of the rare earths. It has been concluded that the ${\mathrm{H}}_2$O molecules separate the positive gadolinium ions from the negative ions and that very possibly the feeble fields to which the gadolinium ion is exposed arise in great measure from the polarized ${\mathrm{H}}_2$O dipoles. Small intervals and large magnetic separations in crystals lead to a "Paschen-Back effect" which is visualized as the incipient uncoupling of the positive ion from the lattice. Since magnetic separations differ along the different axes of the crystal, uncoupling can occur more readily in one direction than in another. No evidence was found for a combination between the oscillation of the ion in the lattice and the frequency of the electronic transition, a possibility imagined by Ehrenfest.