High-precision spectroscopic study of heliumlike iron

The x-ray spectrum emitted by high-velocity heliumlike iron ions has been studied with a crystal spectrometer. The absolute energies of the $n=2\mathrm{}\to n=1\mathrm{}$ lines have been measured with a precision of 40 ppm. A very good agreement has been found between our experimental values and a very accurate multiconfiguration Dirac-Fock calculation. The precision of the measurement and the calculation of the energies are such that for the first time the magnetic correlation energy (spin-spin) as well as the screening of quantum-electrodynamic effects can now be appreciated. The contamination of the considered lines by the so-called dielectronic recombination satellites has been studied in great detail by varying the nature and the thickness of the targets.