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

Abstract

A rigorous quantum electrodynamical calculation is presented for energy levels of the $1 {}^{1}S$, $2 {}^{1}S$, $2 {}^{3}S$, $2 {}^{1}{P}_{1}$, and $2 {}^{3}{P}_{0,1,2}$ states of helium-like ions with the nuclear charge $Z=3,\dots{},12$. The calculational approach accounts for all relativistic, quantum electrodynamical, and recoil effects up to orders $m{\ensuremath{\alpha}}^{6}$ and ${m}^{2}/M{\ensuremath{\alpha}}^{5}$, thus advancing the previously reported theory of light helium-like ions by one order in $\ensuremath{\alpha}$.