Merged electron-ion beam experiments. V. Dissociative recombination of OH⁺, H₂O⁺, H₃O⁺ and D₃O⁺

For pt.IV see ibid., vol.14, no.8, p.1353-671 (1981). Absolute cross sections for dissociative recombination of OH⁺, H₂O⁺, H₃O⁺ and D₃O⁺ have been measured using a merged electron-ion beam apparatus through an energy interval from 0.01 to 1 eV. The recombination cross section for the diatomic OH⁺ is small, one of the smallest measured by the authors for a diatomic ion. The cross sections for the polyatomics H₂O⁺, H₃O⁺ and D₃O⁺ are large and nearly identical. Like most other polyatomic ions they exhibit nearly an E_cm^-1 energy dependence below approximately 0.1 eV. At higher energies the slope of the cross section versus electron energy is much steeper with an energy dependence near E_cm^-2. Cross sections for D₃O⁺ are less than those for H₃O⁺ indicating the presence of a small isotope effect.