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 $E^{\left(\frac{1}{2}\right)}$ behavior, as would be expected for a nearly-free-electron metal, but is somewhat anomalous.