Magnetic and electric dipole transitions between levels of the 4fx configuration perturbed by a static crystalline field are treated. The expression obtained for the pure-electronic electric-dipole transition probability involves matrix elements of an even-order unit tensor between the two 4fx states involved in the transition. The contributions to the transition probability from interactions, via the crystalline field, with the nd94fx−1, 4fx−1nd, 4fx−1ng configurations are shown to add linearly, in such a manner as to multiply each odd k crystal-field parameter Akq by a constant. If ``J mixing'' in the 4fx configuration is neglected ΔJ between the upper and lower 4fx levels is restricted to six units or less. If ``L mixing'' is neglected then ΔL is also restricted to six units or less. Application is made to the fluorescence spectra of PrCl3 and EuCl3. Many of the missing and weak transitions are explained.

Free-ion energy-level schemes for the 4f6 and 4f8 configurations of Eu3+, Sm2+, and Tb3+ are given, which have been calculated from energy matrices including interactions among the three highest multiplicities. The values obtained for the parameters are F2 = 401 cm—1, ζ = 1320 cm—1 for Eu3+; F2 = 330 cm—1, ζ = 1050 cm—1 for Sm2+; and F2 = 434 cm—1, ζ = 1705 cm—1 for Tb3+. The wavefunctions and g values for levels to 40 000 cm—1 are tabulated for Eu3+ and Tb3+. Application of the free-ion wavefunctions to the Stark splitting of EuCl3 and TbCl3 is discussed.

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