Fragmentation of H2O molecules following interaction with slow He2+ ions

The energy distributions of fragments produced in He2+ + H2O collisions at projectile energies ranging from 1 keV up to 5 keV have been investigated experimentally as a function of the detection angle. Two groups of peaks are clearly visible. The first one, which extends up to ∼30 eV, corresponds to Coulomb explosion (CE) of the ionized target (H2O)q+ following electron capture at relatively large impact parameters. At higher energies, a second group corresponds to fast fragments and scattered projectiles produced by quasi-binary collisions. In the analysis, particular attention was paid to these highly energetic ions. In this case, our absolute cross sections dσ/dΩ, differential in the observation angle, are smaller than those predicted by the Rutherford formula. Rather, our experimental values are in good agreement with absolute cross sections calculated using the ZBL potential that implies screening by the bound electrons.