ANALYSIS OF THE CRYSTAL-FIELD SPECTRA OF THE ACTINIDE TETRAFLUORIDES .2. AMF4, CMF4, CM4+CEF4, AND BK4+CEF4

We report a systematic analysis of the crystal-field spectra of four fluoride compounds containing tetravalent actinide ions. The first part of this work [J. Chem. Phys. 95, 7194 (1991)] provided interpretation of the absorption spectra of UF4, NpF4, and PuF4. To extend our analysis to heavier elements of the series, low-temperature absorption spectra of AmF4 and CmF4, and site selective laser-induced emission and excitation spectra of Cm4+:CeF4 and Bk 4+:CeF4 were obtained. A model energy level calculation was found to be in good agreement with the experimental results. It is shown that the crystal-field interaction in combination with spin-orbital coupling results in significant J mixing in the excited states, but ground state wave functions are still relatively pure in J character for the tetravalent actinide ions Am4+, Cm4+, and Bk4+. Trends in the parameters of the effective operator Hamiltonian are compared with those of a Hartree-Fock free-ion model. Interpretation of the ground-state splitting of the nominal S-state ion Bk4+ in CeF4 and color center formation in AmF4 are also discussed. © 1994 American Institute of Physics.