RECOMBINATION MEASUREMENTS AT LOW ENERGIES WITH AU-49-50+,AU-51+ AT THE TSR(,AU)

Recombination of Au49+, Au50+, and Au51+ ions has been studied at the TSR. With Au50+ ions a storage lifetime of only 2 to 4 s was observed with the magnetically expanded electron beam of the cooler at a densit y of n(e) = 10(7) cm(-3). This short storage time is a consequence of the highest recombination rate coefficient ever observed with an atomi c ion (1.8.10(-6) cm(3) s(-1) at zero relative energy E-rel = 0 betwee n electrons and ions). At about 30 meV a huge dielectronic recombinati on resonance is found with a record small width of only about 15 meV. Such resonances fortuitously occurring near E-rel = 0 are probably the main reason for the enhanced recombination rates observed with Au50+, with Pb53+ (in a recent experiment at LEAR) as well as with other com plex ions. For Au49+ and Au51+ the recombination rates are smaller by an order of magnitude.