Theoretical Study of Interesting Fine-Structure Splittings for 2³P_{0, 1, 2} States along Helium Isoelectronic Sequence

Using the multi-configuration Dirac--Fock method including the Breit interactions and QED corrections, we calculate the fine-structure energy levels of the 2³P_{0, 1, 2} states along the helium isoelectronic sequence with atomic number up to Z=36, where LS-coupling is appropriate. Our calculation results agree with the experimental results within about 1%. We elucidate the mechanism of the interesting fine-structure splittings for the 2³P_{0, 1, 2} states along the helium isoelectronic sequence, i.e. the competitions between the spin--orbit interactions and the Breit interactions which represent the relativistic retardation effect of electromagnetic interactions.