Two-electron crystal field analysis in U 4+-doped compounds

Abstract

The utilization of correlation crystal field models for the analysis of 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 usually less satisfactory and the addition of the correlation crystal field is expected to bring some improvements. It has already been utilized for Np 3+ in LaCl 3. In the present work, the spectroscopic data of some U 4+-doped compounds are re-analysed in terms of a crystal model containing one- and two-electron operators. In the examined compounds the actinide ion is coordinated to three types of ligands: oxygen, chlorine and bromine. The re-analysed data are those of uranium-doped ThSiO 4, ZrSiO 4, ThCl 4, α-ThBr 4 and β-ThBr 4 and UCl 4. Adding four to eight two-electron operators (depending on the compound) results in dividing by 2.4 the r.m.s. deviation between the experimental and calculated energy level positions with respect to the standard one-particle parametrization. Systematic trends are sought in order to help the analysis for forthcoming compounds.