Electron-correlation contributions to the amplitudes of two-phonon absorption in f^N systems

Abstract

A theoretical basis for the analysis of the influence of electron correlation upon two-photon transition amplitudes in rare-earth ions has been introduced. The approach is based on the standard perturbation theory and on application of effective operators. It has been shown that in third-order perturbation theory electron-correlation effects are represented by one- and two-particle effective operators. In order to estimate the relative importance of various effective operators, test calculations for the Pr⁺³ ion have been performed.