Investigation of the electronic energy loss of hydrogen ions in H2O: influence of the state of aggregation

The gas-solid difference (phase effect) of the electronic stopping cross section (SCS) is investigated for hydrogen projectiles in H2O at energies near the stopping maximum. We find experimentally, that at low ion velocities the SCS of the gas is considerably higher than that of the solid (up to 15%). This result is discussed in terms of differences between the valence states of H2O vapor and of ice and in terms of the projectile inelastic processes. ((orig.))