Ly- α photon induced amorphization of Ic water ice at 16 Kelvin

Abstract

H2O ice is a ubiquitous material in space, on the surface of planets and their moons, in comets and interstellar dust grains. The structure of H2O ice strongly depends on the deposition temp. It can be amorphous if deposited at low temp., i.e. 16 K, or cryst. if the deposition temp. is >140 K. The structural effects induced by Lyman-a UV photons in cryst. H2O ice was studied by in situ IR spectroscopy. The effects induced by Lyman-a photolysis are compared with those induced by ion irradn. carried out with the same exptl. app. As already obsd. in the case of fast ions, UV Lyman-a photons are able to amorphize the cryst. H2O ice structure after a dose of few eV per mol. This study has astrophys. implications, because photons and fast ions are both present in space, they can induce variations in the profile of the 3 mm band of cryst. H2O ice. These effects have to be considered when 1 attempts to deduce information on the phys. status (e.g. temp. history) of the responsible dust from the profile of the obsd. ice band. [on SciFinder (R)]