Surface4d→4fPhoton Absorption and Surface Mixed Valence in Sm Metal

Abstract

By constant-initial-state photoelectron-yield spectroscopy in the 50-250-eV photon energy range, we have measured separately the $4d\to 4f$ photon absorption of $4f^5$ and $4f^6$ Sm atoms on the surface of evaporated Sm films. The $4f^6$ and $4f^6$ electron emission shows two spectrally distinct enhancements corresponding to $4d^{10}4f^5\to 4d^{9}4f^6$ and $4d^{10}4f^6\to 4d^{9}4f^7$ transitions. Since bulk photon absorption and constant-final-state yield shows only the first spectrum, surface and bulk electronic configurations can be distinguished.