Orbital-collapse effects in photoemission from atomic Eu

Resonant photoelectron spectra of atomic Eu have been measured in the photon-energy ranges of the ''4d→4f '' (110-170 eV) and 3d→4f (1120-1165 eV) excitations. For the ''4d→4f '' giant resonance, the decay process results mostly in Eu+ main-line configurations, including some fractional enhancement directly into the 4d continuum. The 3d→4f excitations, however, are characterized by competition between the main-line decay channels and channels corresponding to highly excited (satellite) ionic states. We find that decay after 4d excitation leads predominantly to the 4f continuum, whereas several channels participate in the decay following 3d excitation. The observed decay characteristics are discussed with regard to orbital-collapse phenomena