Photoemission from transition metals and their compounds

Photoemission experiments on 3d transition metals are reviewed. The emphasis is on understanding the results of experiments, not on experimental details and methods. Extensive use is made of simple models. Much of the review pertains to resonances associated with the autoionization 3p53dn+1 →3p63dn−1 +e and their implications for electronic structure. Nonresonant ultraviolet and x-ray photoemission spectroscopies are also discussed. Photoemission and photoabsorption of transition-metal atoms are discussed first. Results for Mn are described at length to establish the validity of the autoionization mechanism. The results from atomic spectroscopy are used to interpret experiments on solids. The role of atomiclike excitations in solids is examined. Compounds of transition metals are analyzed in terms of ligand-field theory, which is shown to be inadequate. Newer theories involving configuration interaction are shown to agree better with experiment. Various mechanisms for the excitation of photoemission satellites are presented. In the metallic state, effects similar to those observed for the compounds occur. The existence of two-bound-hole final states is demonstrated. Their importance in Auger spectroscopy, valence- and core-emission satellites, and resonant photoemission is discussed. The effects of closely related electron correlations on the band structure are described.