Storage ring study of the dissociative recombination of He+2

Absolute cross sections for dissociative recombination have been measured for the He-4(2)+ and (HeHe+)-He-3-He-4 isotopomers as a function of storage time at the ASTRID 2 storage ring. The recombination rate of (HeHe+)-He-3-He-4 with low-energy electrons is found to dramatically decrease with time, giving an upper limit for the thermal rate coefficient for cold ions of the order of 6 x 10(-10) cm(3) s(-1), in agreement with flowing afterglow measurements. Two-dimensional imaging of the atomic fragments points to He(1s(2) S-1) + He(1s3s S-3) as the lowest dissociation channel to be accessed in the dissociative recombination of rovibrationally hot ions.