ION-BEAM INDUCED AMORPHIZATION OF CRYSTALLINE WATER ICE

New experimental data demonstrate the transition from crystalline to amorphous water ice induced by keV ion irradiation at temperatures between 10 and 100 K. IR spectroscopy has been used for the << in situ monitoring >> of the structural changes. It is shown that the ion-beam-induced amorphization of crystalline water ice is a very effective process. Each H2O molecule transformation requires an energy deposited of the order of (2 divided-by 10) eV, for temperature increases from 10 to 100 K. The cross-section for the process has been evaluated. At temperatures above 55 K the crystalline water ice is quite resistant to ion irradiation because the unstable products like radicals produced during ion irradiation of ice are mobile, can recombine and be desorbed, thus restoring the original crystalline structure.