Interference between radiative emission and autoionization in the decay of excited states of atoms

An excited state of an atom which can autoionize can also undergo radiative decay. We consider the interaction between the final states resulting from these two modes of decay, and its effects on such quantities as the fluorescence yield of the excited state, excitation profile of the excited state, and the spectra of the emitted photons and electrons. It is shown that the fraction of decays of the excited state resulting in a photon (fluorescence yield) is particularly sensitive to the details of the final-state interaction. In lowest order in the final-state interaction, the fluorescence yield is increased by a factor $(1+\frac{1}{q^2})$ from the traditional value, where $q$ is the Fano $q$ parameter relating to the excited state and the final atomic state.