Enhanced Multielectron Effects in the Core-Level Spectra of Calcium, Strontium, and Barium

Intrinsic collective losses are observed in the core-level spectra of Ca, Sr, and Ba that exceed those observed in Al, Mg, and Na by factors up to 10. The coupling strength depends on the nature of the core hole. The relationship between the strength of the collective excitations and the extraatomic relaxation energies explains increases of 1.0 eV and 0.3 eV in Ca $3p$ and Sr $3p$ splittings compared to the free-ion spin-orbit splittings.