The authors present a formalism which describes the X-ray photoemission (XPS) process and the following Auger decay as one quantum mechanical event. This can lead to a nonLorentzian broadening of the XPS spectrum. They discuss the validity of a two-step model where the XPS and Auger processes are treated as independent. Sum rules for the Auger spectra are derived and it is shown that these predict that the relative weights of the Auger peaks depend strongly on the lifetime of the XPS hole. They treat the plasmon gain satellites in free-electron like metals and trace the unusual shape of these peaks to interference effects. Finally, Auger-photoelectron coincidence spectroscopy (APECS) is considered. For a finite system, APECS can give information about the spatial properties of the excited states, while it is harder to obtain such information for a system with a continuous spectrum.
 

AIP Conference Proceedings, 517-29, 1982.