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Abstract:
The central and new aspect of this paper is the interference in core level spectra between mixed valence features and screening mechanisms. We investigated the 3d and 4d X-ray photoelectron spectra (XPS) of Ce atoms in CePd3 (where configuration mixing has been established by other methods), CeSe (which is known to contain only Ce3+ with the spectra of CeCu2Si2 and CeAl2. Even in the cases with a stable 4f1 configuration, the Ce 3d spectra are found to contain so-called shake down (4f2) contributions as a result of the change of the initial 4f configuration due to screening of the 3d final state hole. Therefore, only qualitative lower limits for the mixed valence ratio Ce3+:Ce4+ can be derived from the XPS core level spectra. These ratios are ≈10:1 for CeCu2Si2 and ≈5:1 for CeAl2. The multiplet splittings and shake down probabilities for core level XPS peaks of Ce are found to be strongly dependent upon chemical environment.
