TOWARDS A PRECISION SPECTROSCOPY OF VERY HIGHLY-CHARGED IONS BY EMPLOYING DIELECTRONIC RECOMBINATION

The measurement of dielectronic recombination (DR) with high energy resolution provides a unique tool for precision spectroscopy of intermediate doubly excited states of very highly charged ions. One of our experimental goals at the experimental storage ring (ESR) of GSI is the determination of the 2(1/2)2p(1/2) energy splitting epsilon in high-Z Li-like ions. This requires electron-ion center-of-mass energies for DR measurements up to about 300 eV, which is not easily accessible with the cooling device of the ESR as long as it has to guarantee the cooling of the stored ion beam. In a new experiment with 150 MeV/u AU(76+) We were able to extend the accessible energy range to a maximum of about 300 eV, which requires a variation of the electron laboratory energy of up to 10 keV. New experimental data for recombination of U89+ and Au76+ ions were obtained. In particular, the group of (2p(3/2)6l) resonances in e + Au76+(1s(2)2s) collisions could be completely observed with good energy resolution. In addition, the first resonances of the (2p(1/2)nl) Rydberg sequence with n = 20 to n = 26 were measured. By an extrapolation of the resonance energies to n = infinity, i.e. to the series limit, the energy epsilon can be determined.