Classical dynamics study of the ion bombardment of ice

A classical dynamics model is used to simulate the bombardment of ${\mathrm{H}}_2$O ice by ${\mathrm{O}}^{+}$ ions at energies between 23 and 115 eV. These energies are appropriate to describe the erosion processes occurring on the inner moons of Saturn. The total erosion yields vary between 0.83 and 2.28 ${\mathrm{H}}_2$O equivalents per incident ion in the energy range investigated. The majority of the ejected material is intact ${\mathrm{H}}_2$O molecules which have very little internal energy. Clusters of the type (${\mathrm{H}}_2$O${)}_{\mathrm{n}}$ are observed in the calculations. Clusters of the form (${\mathrm{H}}_2$O${)}_{\mathrm{n}}$ ${\mathrm{H}}^{+}$, however, are not observed. This is consistent with experimental results of others on cluster and fragment formation. Predictions made by a collision-cascade model for the absolute erosion rates of ejected species are shown to be inappropriate for these low impact energies.