Direct measurements of 2{sup 3}S - 2{sup 3}P energies in high-Z heliumlike ions

We present results of new measurements of the 1s2s {sup 3}S{sub 1} - 1s2p {sup 3}P{sub 0,2} fine structure transition energies in helium-like argon, Ar{sup 16+}. Precision measurements of these energy intervals in two-electron ions provide sensitive tests of calculated Z{sup 4}-dependent relativistic contributions to the 2p {sup 3}p level energies. We have performed spectroscopic wavelength measurements of these vacuum ultraviolet transitions using high resolution grating spectroscopy and position-sensitive detection of a foil-excited fast beam of argon ions at the ATLAS accelerator facility. Comparison of preliminary results with recent accurate relativistic calculations will be presented. The final experimental results are to measure the 2s-2p transition energies to {approximately}10 ppm [{approximately}0.03(Z{alpha}){sup 4} a.u.], which tests the relativistic contributions to {approximately}0.01% and the QED corrections to {approximately}0.2%.