MEASUREMENTS OF 2S-S-2(1 2)-2P-P-2(3/2,1/2) TRANSITION ENERGIES IN LITHIUM-LIKE HEAVY-IONS - EXPERIMENTS AND RESULTS FOR NI25+ AND ZN27+/

Wavelengths of the fine-structure transitions 2s S-2(1/2)-2P P-2(3/2) and 2s S-2(1/2)-2p P-2(1/2) in lithiumlike Ni25+ and Zn27+ have been m easured using beam-foil excitation and grazing-incidence spectroscopy. The respective transition wavelengths of 142.461 +/- 0.006 Angstrom a nd of 216.061 +/- 0.011 Angstrom for Zn27+ have not been measured so f ar and present the most precise values in lithiumlike heavy ions measu red by beam-foil spectroscopy. The Ni25+ results are in very good agre ement with data from grazing-incidence spectroscopy at tokamaks. The m easurement precision for both ions corresponds to less than or equal t o 1% of the quantum electrodynamic contributions to the transition ene rgies. This provides sensitivity to two-photon exchange processes for the screening of the electron self-energy. [S1050-2947(98)04310-8].