Spectroscopic Tests of Quantum Electrodynamic Effects in Two-Electron Ions.

Precision wavelength measurements of the 1s2s ('3)S(,1) - 1s2p ('3)P(,0,2) transitions in two-electron sulfur and titanium have been performed using the fast -ion spectroscopy technique. The photon emission for these transitions was observed in the vacuum ultraviolet region, using a one-meter normal incidence spectrometer and a windowless photon detector. The results are 673.428 (+OR-) 0.017(ANGSTROM) for ('3)S(,1) - ('3)P(,2) and 756.315 (+OR-) 0.030(ANGSTROM) for ('3)S(,1) - ('3)P(,0) in sulfur, and 389.48 (+OR-) 0.07(ANGSTROM) for ('3)S(,1) - ('3)P(,2) in titanium. The measurements in sulfur are of improved precision from previous results, and the measurement in titanium is the first one performed in that ion. The precision obtained is sensitive to current theoretical calculations of relativistic and quantum electrodynamic effects in two-electron systems. The results for the ('3)S(,1) - ('3)P(,2) measurements show consistent agreement with other experiments and theory along the isoelectronic sequence. The result of the ('3)S(,1) - ('3)P(,0) measurement in sulfur is in slight disagreement with theory, and consistent with other two-electron measurements of this transition in helium-like ions.