UNRESOLVABLE RYDBERG LINES IN X-RAY-ABSORPTION SPECTRA OF FREE ATOMS

We investigate the contribution of the unseparated Rydberg states whic h are usually neglected, in atomic K-edge x-ray spectra. We suppose th at the core hole broadening is large, so that the global contribution of all unresolved Rydberg levels introduces an apparent threshold shif t with a value nearly equal to the separation of the first unresolvabl e Rydberg line from the series limit. The apparent threshold has the s ame dependence on the photon energy as the true one. The region of unr esolvable Rydberg lines can be described by means of a quasi-particle approach, by introducing a pseudo-wave vector formalism. We perform an analysis of Ne and Ar K-edge absorption spectra. Using the present th eory, we derive a very simple procedure for the evaluation of the inst rumental and the core hole broadening in x-ray spectra.