Autodissociation of doubly charged water molecules

The electron impact dissociative double-ionization cross sections for H2O between 45 and 1500 eV have been measured using time of flight mass spectrometry. The energy dependence of the H++OH+ and H++O+ ion pair production cross sections indicate that Auger-like autoionization following a vacancy in the 2a(1) molecular orbital is the main double ionization channel at high velocities. In contrast to expectation, these findings show that dissociation through the H2O2+ precursor state is a significant process at high collision energies. Knowledge of this process is vital as it has a direct affect on the production of important molecular species, such as H-2, during water radiolysis. Branching ratios of the various fragments produced following both autoionization and double ionization have also been obtained.