Study of the energy level structure for ions of the thallium isoelectronic sequence

The structure of the energy level diagram for 30 ions of the thallium isoelectronic sequence is studied on the basis of the relativistic Dirac-Fock self-consistent field method with the configuration interaction taken into account. It is discovered that the ground-state configuration and the lowest term change along the thallium isoelectronic sequence: At the beginning of the sequence, the ground-state configuration is 6s ²6p, and it becomes 6s ²6f beginning from the Cf¹⁷⁺ ion. On the basis of theoretical calculations, the ground-state ionization potentials are determined for each ion. The influence of interaction of the 6s6p ² configuration with the 6s ²6d configuration on the ² D _{3/2, 5/2} levels of the latter was also studied, and values of the fine-structure splitting of the 6s ²6p ² P ⁰ and 6s ²6d ² D levels were determined for the Tl-like ions considered.