High-resolution X-ray absorption spectroscopy as a probe of crystal-field and covalency effects in actinide compounds

Abstract

Applying the high-energy resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS), we were able to probe, for the first time to our knowledge, the crystalline electric field (CEF) splittings of the5fshell directly in the HERFD-XAS spectra of actinides. Using ThO2as an example, data measured at the Th 3dedge were interpreted within the framework of the Anderson impurity model. Because the charge-transfer satellites were also resolved in the HERFD-XAS spectra, the analysis of these satellites revealed that ThO2is not an ionic compound as previously believed. The Th6doccupancy in the ground state was estimated to be twice that of the Th5fstates. We demonstrate that HERFD-XAS allows for characterization of the CEF interaction and degree of covalency in the ground state of actinide compounds as it is extensively done for 3dtransition metal systems.