Relativistic many-body calculations of energies for doubly-excited 1s2l2l′ and 1s3l3l′ states in Li-like ions

Abstract

Energies of 1s2l2l′ and 1s3l3l′ states for Li-like ions with Z = 6–100 are evaluated to second order in relativistic many-body perturbation theory. Second-order Coulomb and Breit–Coulomb interactions are included. The calculations start with a Dirac potential and include all possible 1s2l2l′ and 1s3l3l′ configurations. Correction for the frequency dependence of the Breit interaction is taken into account in lowest order. The Lamb-shift correction to the energies is also included in lowest order. A detailed discussion of the various contributions to the energy levels is given for Li-like iron (Z = 26). We found that the three-electron corrections to the energy contribute about 10–20% of the total second-order energy. Comparisons are made with available experimental data and excellent agreement for term splitting is obtained even for low-Z ions. These calculations are presented as a theoretical benchmark for comparison with experiment and theory.PACS Nos.: 32.30.Rj, 32.70.Cs, 31.25.Jf, 31.15.Md