Cosmic ray sputtering yield of interstellar ice mantles: CO and CO2 ice
  thickness dependence
  Cosmic-ray-induced sputtering is one of the important desorption mechanisms
at work in astrophysical environments. The chemical evolution observed in
high-density regions, from dense clouds to protoplanetary disks, and the
release of species condensed on dust grains, is one key parameter to be taken
into account in interpretations of both observations and models. This study is
part of an ongoing systematic experimental determination of the parameters to
consider in astrophysical cosmic ray sputtering. As was already done for water
ice, we investigated the sputtering yield as a function of ice mantle thickness
for the two next most abundant species of ice mantles, carbon monoxide and
carbon dioxide, which were exposed to several ion beams to explore the
dependence with deposited energy. These ice sputtering yields are constant for
thick films. It decreases rapidly for thin ice films when reaching the
impinging ion sputtering desorption depth. An ice mantle thickness dependence
constraint can be implemented in the astrophysical modelling of the sputtering
process, in particular close to the onset of ice mantle formation at low visual
extinctions.
