Absolute dielectronic recombination cross sections of hydrogenlike helium

We have measured the {Δ}N=1 dielectronic recombination cross sections of hydrogenlike helium. Recombination rates were investigated as He⁺ ions interacted with free electrons in the electron-cooler section of an ion storage ring. The ion beam was cooled prior to recombination, resulting in enhanced energy resolution. Fits to the 2l2l' resonances yielded transverse and longitudinal temperatures of kT_⊥=0.15 eV and kT_∥=0.8×{}10^-4 eV, respectively. The resulting peak widths are approximately 0.3-eV full width at half maximum. The measured integrated cross sections are in qualitative agreement with calculated resonance strengths.