Energy Levels of PrCl3

A review of the spectra of the Pr³⁺ ion in PrCl₃ is presented and the spectra are reanalyzed by means of a more complete Hamiltonian than has been previously used. This new Hamiltonian includes a complete calculation of the crystalline field interaction for a field of D_3h symmetry, and the first‐order calculation of the orbit‐orbit, mutual spin‐orbit, and spin‐spin interactions, as well as the usual spin‐orbit and mutual electrostatic interactions. The multiplet splitting and crystalline field splitting are treated separately according to a least‐squares procedure; the standard deviation of the center of gravity of the multiplets is 200 cm^—1 without the orbit‐orbit interaction and 105 cm^—1 with the orbit‐orbit interaction. The values of F₂, F₄, F₆, ζ, and α are 305.4, 51.88, 5.321, 729.5, —, cm^—1, respectively, in the first case, and 307.9, 50.23, 5.033, 755.1, —0.6542, cm^—1, respectively, in the second case. The standard deviation of the calculation for 40 of the crystalline field levels is 7 cm^—1. If the deviation of the ¹D₂ levels, which fit the calculation particularly badly, are not included, the standard deviation is then only 4 cm^—1. The values of the crystalline field parameters are: $A_{20}{\mathrm{\hspace{0.17em}〈r}}^2{\text{〉=47.26,A}}_{40}{\mathrm{\hspace{0.17em}〈r}}^4{\text{〉=−40.58,A}}_{60}{\mathrm{\hspace{0.17em}〈r}}^6{\text{〉=39.62,A}}_{66}{\mathrm{\hspace{0.17em}〈r}}^6\text{〉=26.67\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ .