Physical Review B
Photoemission spectra from the shallow 3p3/2 core levels of the surface atoms of metallic potassium exhibit the effects of a small but measurable crystal-field splitting of ∼38 meV. It manifests itself mainly as an apparent angle-dependent modulation of the spin-orbit splitting. This phenomenon may, in general, interfere with accurate determinations of surface-atom core-level shifts.
"Evidence for Crystal-Field Splitting in Surface-Atom Photoemission from Potassium," G. K. Wertheim and D. M. Riffe, Phys. Rev. B 52, 14906 (1995).