The sputtering coefficients or erosion yields of frozen gases and other nonconducting materials due to irradiation by fast ions have been shown to be considerably larger 1 " 5 than predicted based on the "standard" sputtering theory, which has been applied so successfully to metals. 6 Whereas sputtering in metals is determined by the energy deposited in elastic nuclear collisions, it has been shown conclusively that the erosion of frozen gases, 1,3 » 5 alkali halides, 2 ' 4 and certain insulators 7 by fast ions is determined by energy deposited in the material through electronic processes.Because of the relatively high diffusivity of electrons (for metals) and electrons and holes (for semiconductors), electronic excitation rapidly diffuses from its origin around the track of a fast ion and, by the time it is transformed into atomic motion, it is too dilute to displace atoms of a solid. For insulators this is not the case. The electronic excitation is produced and retained in sufficiently localized states to result in production of point defects in the alkali halides 8 and 118, 175 (1976) [Sov.ejection of ions from insulating surfaces as observed by electron-and photon-stimulated desorption. 9 ' 10 The excitations can also lead to even more massive atomic displacements as in track formation by energetic ions in insulators 11 and erosion of ice films as in the current experiments.We have studied the temperature dependence of the erosion of H 2 0 ice below 160 °K to determine the mechanisms of erosion produced by electronic processes. A clear temperature dependence has been reported for the ion induced erosion of solid Xe and attributed to a thermal evaporation process. 3 A temperature dependence was also observed in the sputtering of alkali halides by both ions 2 ' 4 and electrons. 12 ' 13 The erosion yield, which increased exponentially with temperature, was interpreted as due to the diffusion of radiation produced color centers to the surface. 2 ' 13 In the present experiments on the erosion of H 2 0 ice we find two distinct temperature regions. These depend quite differently on dE/dx, the electronic energy loss of the fast ions per unit path length, The erosion of water ice films by fast H and He ions has been found to depend on the electronic energy loss of the ion. At low temperatures the erosion yield is temperature independent and varies quadratically with the electronic stopping power, consistent with a Coulomb repulsion model of ejection. At temperatures above ~100 °K the erosion is found to be temperature dependent and linear with the electronic stopping power" The erosion in this regime can be associated with defect formation and migration in the ice.

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