2-ELECTRON CRYSTAL-FIELD ANALYSIS IN U4-DOPED COMPOUNDS()

The utilization of correlation crystal field models for the analysis o f experimental spectra is developing for lanthanides. These models are useful to improve the fits for the few levels which are badly fitted by the standard model. For actinides the crystal field simulation is u sually less satisfactory and the addition of the correlation crystal f ield is expected to bring some improvements. It has already been utili zed for Np3+ in LaCl3. In the present work, the spectroscopic data of some U4+-doped compounds are re-analysed in terms of a crystal model c ontaining one- and two-electron operators. In the examined compounds t he actinide ion is coordinated to three types of ligands: oxygen, chlo rine and bromine. The re-analysed data are those of uranium-doped ThSi O4, ZrSiO4, ThCl4, alpha-ThBr4 and beta-ThBr4 and UCl4. Adding four to eight two-electron operators (depending on the compound) results in d ividing by 2.4 the r.m.s. deviation between the experimental and calcu lated energy level positions with respect to the standard one-particle parametrization. Systematic trends are sought in order to help the an alysis for forthcoming compounds.