Dynamical theory of Auger processes

The quadratic response formalism is used to derive a general expression for the Auger electron current in the limit of high energies of both photo- and Auger electrons. The Auger decay of the initial core hole is treated to all orders in the decay rate. General formulas for the first and second moments of the Auger spectra are derived, and simple results are obtained for limiting cases. We show that the center of gravity of the spectra depends strongly on the lifetime of the initial core hole. The competition between different Auger processes can cause dramatic changes in the position and shape of the peaks in the spectra. It is also shown that the Auger decay can lead to a broadening of the photoelectron spectra that cannot be represented by a Lorentzian convolution. We discuss the validity of the two-step model for which the Auger decay is assumed to be decoupled from the creation of the initial core hole.