Dissociative Recombination of H₃O⁺, HD₂O⁺, and D₃O⁺

We present an experimental study of the dissociative recombination (DR) of H3O+ and its isotopomers D3O+ and HD2O+ performed at the ASTRID storage ring. DR cross sections have been measured as a function of energy, while complete branching ratios have been measured at E = 0. The H3O+ data yield an accurate determination of the branching ratio for water formation (0.25 ± 0.01). The three molecular ions—H3O+, D3O+, and HD2O+—show a marked resemblance concerning cross sections and branching ratios. The only observed isotope effect is in the fragmentation pattern of HD2O+, where the release of a light fragment is favored over release of a heavier fragment. As a consequence, an enhanced production of deuterated molecules takes place as a result of the DR process.