Mixing-Decay Widths for4fIons in Solids

The intrinsic lifetime width in x-ray photoemission spectroscopy, due to mixing decays, is shown to decrease rapidly as a function of the number of $4f$ electrons. In a system near configuration crossover, mixing decays may also strongly broaden (or render unobservable) ionic resonances at frequencies as low as the far infrared; this is illustrated by model calculations for Sm and Eu salts.