Relativistic many-body calculations of energy levels and of fine-structure intervals in the caesium atom

Abstract

The many-body perturbation theory is used for relativistic calculations of energy levels and of fine-structure (FS) intervals for the 6s, 7s, 8s, 6p, 7p, 5d, 6d and 4f states of Cs. The second-order correlation corrections in the residual Coulomb interaction are calculated taking into account all intermediate configurations of a discrete and continuous spectrum with orbital angular momentum of each electron l<or=5. The wavefunctions and energies in the zeroth approximation are obtained by the relativistic Hartree-Fock (RHF) method. The correlation corrections substantially improve the agreement between the calculated and experimental values. The calculated values of the FS intervals are the following (in cm-1): 556 (6p), 185 (7p), 63 (5d), 48 (6d), and -0.180 (4f). The experimental data are: 554; 181; 97.6; 42.9; -0.1813, respectively. The mechanisms of fine splitting in Cs are discussed.