Abstract
We have measured the 1s2s S-3(1)-1s2p P-3(0) and 1s2s S-3(1)-1s2p P-3(2) fine structure transition wavelengths in the helium-like Ar16+ ion, using the beam-foil spectroscopy technique with position-sensitive photon detection. The wavelength results have precisions of < 30 ppm and are sensitive to the total QED corrections to < 0.5%. The measurements confirm the significance of (Z alpha)(4)-dependent relativistic corrections to the n = 2 state fine structures suggested by recent calculations. The small remaining discrepancies between these measurements and the accurate theoretical values suggest that the magnitude of uncalculated higher order QED terms is about 0.15(Z alpha)(4) a.u. The status of our experimental search for the(3)S(1)-P-3(0) transition in Ni26+ is discussed.