CORRELATION-EFFECTS IN THE CORE EXCITATION-SPECTRA OF RYDBERG ATOMS WITH LARGE ORBITAL MOMENTUM

The inner electron in the two-electron atom is excited in the presence of a high Rydberg electron with large orbital momentum. In the initial state the electrons are assumed to be non-correlated. In the final state the Rydberg electron moves in the field of the excited core with degenerate levels. This leads to the appearance of electron-electron correlations. The most important part of them is taken into account in the approximation where only the dipole term is retained in the multipole expansion of the electron-electron interaction. The positions and strengths of the lines in the excitation spectra are calculated. The factorization of the transition matrix element typical to the ICE (independent core excitation) picture is shown to be retained. The outer (Rydberg) electron transition is described by the overlap (shake-off) radial matrix element. These are not essentially influenced by the long range interaction with the core. In the asymptotic case of large total orbital momentum L, the outer electron orbital momentum l1 in the final state is well defined; that is it is expressed in the simple pattern of the core excitations spectra. The transition to the more complicated regime of strong l1 mixing as L decreases is traced and related qualitatively with recent experimental observations. The onset of strong l1 mixing remains the same in the presence of a non-Coulombic core.