COHERENT AND INCOHERENT PROCESSES IN RESONANT PHOTOEMISSION

The basis for resonant photoemission is discussed in connection with d ata for a physisorption system, Ar/Pt(111) and a 3d transition metal, Ni(100). For Ar/Pt(111) the quasi-localized character of the intermedi ate state leads to two types of features in the autoionization spectra , showing resonant Raman and normal Auger-like behaviour, respectively . For Ni(100) resonant Raman behaviour is observed in photoemission be low the L-3 threshold. At threshold, the emission feature changes char acter and after a rather narrow transition region it appears at consta nt emission energy instead. Clear signatures of interference between t he direct photoemission and autoionization channels are identified.