Dissociation of water molecules upon keV H+- and Heq+-induced ionization

The interaction of keV H+, He+ and He2+, ions with gas-phase H2O molecules leads to formation of H2Oq+ ions which subsequently can undergo dissociation into various fragment species. From coincident determination of the fragmention kinetic energies, kinetic energy releases (KER) for the different dissociation channels are obtained. We present the KER values for the various dissociation channels at different projectile kinetic energies. For He+, extraordinarily large relative dissociation yields are observed as compared to H+ and He2+. For both singly charged projectiles we observe 14.5 eV H+ fragments, most probably due to the two-step H2O2 -> HO2+, + H -> H+ + O+ +H process predicted 5 years ago (Nobusada K and Tanaka K 2000 J. Chem. Phys. 112 7437).