Spectroscopy of highly doubly-excited states of helium through dielectronic recombination

We report a spectroscopic determination of dielectronic recombination resonances with hydrogen-like helium. An energy resolution of 0.3 eV FWHM was achieved through the use of a cooled ion beam in the CRYRING storage ring. First theoretical results, including correlation to all orders, for the Delta n=1 and Delta n=2 resonances are presented. Unexpectedly, it was found that the Delta n=2 resonances are dominated by certain 3 F 0 doubly-excited states, in contrast to the results for Delta n=1 transitions.