Fine structure of the 2 3P state in helium‐like sulfur and chlorine

We present precision measurements of the 1s2p (3P2 ‐ 3P0) fine structure energies in the helium‐like ions S14+ and Cl15+. The fine structures are obtained from spectroscopic measurements of the 1s2s 3S1 ‐ 1s2p 3P0,2 transition wavelengths. These results represent the most precise experimental determinations of the helium‐like J=2 ‐ 0 intervals for Z≳5. They establish the magnitude of missing higher order relativistic contributions in previous high‐Z calculations of this fine structure, and they are in excellent agreement with new relativistic many‐body calculations.