Dissociative recombination and excitation of H2O+ and HDO+

Dissociative recombination and excitation of H2O+ and HDO+ in the vibrational ground state have been studied at the heavy-ion storage ring ASTRID. Absolute cross sections have been measured in the energy range from similar to 0.1 meV to similar to 50 eV. The total cross sections for dissociative recombination are essentially the same for the two molecular ions. Complete branching ratios for all possible product channels in dissociative recombination at E = 0 have been determined. Three-particle breakup accounts for similar to 60% of the recombination events. With HDO+,recombination into OD + H is twice as probable as recombination into OH+D. An isotope effect is also evident in the cross sections for dissociative excitation of HDO+, where H+ production is more likely than D+ production. [S1050-2947(99)01910-1].