X-ray photoemission from sodium and lithium

X-ray photoelectron spectra of Na and Li metals were obtained in ultrahigh vacuum. Rich plasmon structures were observed on all peaks. Both the photoemission and Auger peaks showed large extra-atomic relaxation energies. A simple "equivalent-cores" screening model predicts extra-atomic relaxation energies in good agreement with experiment. The Na valence band shows approximately a E(12) behavior, as would be expected for a nearly-free-electron metal, but is somewhat anomalous. © 1973 The American Physical Society.