Electron impact single ionization and dissociative excitation of H3O+, HD2O+ and D3O+

First absolute cross sections for electron impact single ionization of H3O+, HD2O+ and D3O+ and for dissociative excitation (DE) producing H+ and D+ are reported. The animated crossed electron-ion beam method has been employed in the energy range from threshold to 2500 eV. The maxima of these cross sections are found to be unusually small (<1 x 10(-17) cm(2)). The ionization threshold energies are determined to be 24.7 +/- 0.5, 24.4 +/- 0.5 and 24.0 +/- 0.5 eV for H3O+, HD2O+ and D3O+, respectively. The observed DE threshold energies lie in the range 10-12.5 eV and the maximum kinetic energies released are between 3 and 4 eV. Significant differences are observed between the results obtained for the three isotopomers.