Electronic sputtering of condensed ${\mathrm{O}}_2$

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.