Interesting Features of n^2D Rydberg Series Fine-Structure Splittings along the Sodium-Like Isoelectronic Sequence

Using a simplified multi-configuration Dirac--Fock (SMCDF) scheme based on the multi-configuration Dirac--Fock (MCDF) theory, we study the systematic variations of the fine-structure splittings of n²D_3/2,5/2 Rydberg series along the sodium-like isoelectronic sequence, i.e. the fine-structure orderings vary with increasing atomic number Z. The competition between the spin-orbit interactions and the exchange interactions due to relativistic effects of the nd orbital wavefunctions well explain such variations. Furthermore, the effect of Breit interactions which plays the secondary role is studied.