Electronic sputtering of condensedO2

The electronically induced sputtering of solid oxygen films has been measured using helium and hydrogen ions with energies from 0.3 to 3.5 MeV. The sputtering yield exhibits a linear dependence on (dE/dx${)}_e$, the electronic stopping power of the ions, at low (dE/dx${)}_e$, with a transition to an approximately quadratic dependence at high (dE/dx${)}_e$. These results are similar to those found for solid ${\mathrm{N}}_2$ but differ from those for solid CO. The electronic sputtering yield of oxygen has also been measured as a function of the angle of incidence of singly charged and charge-state-equilibrated helium ions at 2 MeV. The angular dependence of the yield is approximately (cosθ${)}^{\mathrm{-}1.6}$ and is essentially the same for both the singly charged and equilibrated ions, although the absolute yields are a factor of 1.2 higher for the charge-state-equilibrated ions. The measured angular dependence in the quadratic sputtering regime is remarkably well accounted for by a model of diffusive energy transport to the surface and sputtering by a collective process.