ORIGIN OF THE LOW-ENERGY COMPONENT AND ISOTOPE EFFECT ON DISSOCIATIVE RECOMBINATIONS OF HEH+ AND HED+

Dissociative recombination of HeD+ was studied using a storage ring and compared with the results on HeH+. A strong peak at around 20-eV electron energy was observed in addition to a peak at nearly zero energy. Their shapes are very similar to corresponding ones on HeH+. The relative strengths of these peaks, however, are quite different between HeH+ and HeD+, which is clear evidence of isotope effect. By mixing O2 gas into the helium hydride ion source, it was confirmed that the peaks originate from the ground state of molecular ions. The dissociation energy for the low-energy peak was about 1 eV. This implies that the dissociation of the low-energy component occurs primarily to He + H* (n = 2), although the possibility of some branching to n = 1 cannot be excluded.