N4,5 excitations in metallic cesium. Single‐electron behaviour and collective effects

The N4,5 excitation spectrum of Cs is measured with yield spectroscopy from the onset of transitions at 77 to 180 eV photon energy. Synchrotron radiation served as a light source. A broad maximum due to delayed transitions to f‐symmetric continuum states is the dominating feature of the spectrum. An indication for existence of localized f‐symmetric final states is found. Above the N4,5 edges at (77.1 ± 0.1) and (79.3 ± 0.1) eV photon energy transitions to p‐symmetric extended metal states are observed. Their qualitative agreement with APW band structure calculations is discussed. EDC's obtained with photon energies 75 and 111 eV are presented. The observed asymmetric shape of the 4d photoemission maxima in the EDC's and the shape of the N5 edge are discussed with regard to the final state interaction theory by Mahan, Nozieres, and de Dominicis.