Autodissociation of doubly charged water molecules

Abstract

The electron impact dissociative double-ionization cross sections for H2 O between 45 and 1500 eV have been measured using time of flight mass spectrometry. The energy dependence of the H+ +O H+ and H+ + O+ ion pair production cross sections indicate that Auger-like autoionization following a vacancy in the 2 a1 molecular orbital is the main double ionization channel at high velocities. In contrast to expectation, these findings show that dissociation through the H2 O2+ 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 H2, during water radiolysis. Branching ratios of the various fragments produced following both autoionization and double ionization have also been obtained.