Angle-resolved photoemission from crystal-field-split adatom levels

Abstract

We investigate the angular distribution of photoelectrons emitted from atoms physisorbed on the surface of a metal. The crystalline electric field of the surface is represented by a small number of point charges in the vicinity of the adatom, and the splittings of $p$ and $d$ adatom levels in the crystal field are calculated. The spin-orbit splitting of the adatom states is assumed to be large in comparison with the crystal-field effects. For adatom $p$ levels we consider both fourfold and bridge sites on a (100) surface of an fcc or bcc metal, and we include results for $d$ states in the fourfold configuration. Within the dipole approximation photoelectron distributions are calculated for these cases assuming normally incident, unpolarized light. The results demonstrate that the angular distributions are sensitive to substrate geometry. Implications of this work for recent ultraviolet photoemission experiments involving xenon and mercury adsorbed on a tungsten surface are discussed.