Theoretical energies of low-lying states of light helium-like ions

A rigorous quantum electrodynamical calculation is presented for energy levels of the 1 ¹S, 2 ¹S, 2 ³S, 2 ¹P₁, and 2 ³P0,1,2 states of helium-like ions with the nuclear charge Z=3,,12. The calculational approach accounts for all relativistic, quantum electrodynamical, and recoil effects up to orders mα⁶ and m²/Mα⁵, thus advancing the previously reported theory of light helium-like ions by one order in α.