Efficiency of non-thermal desorptions in cold-core conditions. Testing
  the sputtering of grain mantles induced by cosmic rays
  Under cold conditions in dense cores, gas-phase molecules and atoms are
depleted from the gas-phase to the surface of interstellar grains. Considering
the time scales and physical conditions within these cores, a portion of these
molecules has to be brought back into the gas-phase to explain their
observation by milimeter telescopes. We tested the respective efficiencies of
the different mechanisms commonly included in the models. We also tested the
addition of sputtering of ice grain mantles via a collision with cosmic rays in
the electronic stopping power regime. The ice sputtering induced by cosmic rays
has been added to the Nautilus gas-grain model while the other processes were
already present. Each of these processes were tested on a 1D physical structure
determined by observations in TMC1 cold cores. The resulting 1D chemical
structure was also compared to methanol gas-phase abundances observed in these
cores. We found that all species are not sensitive in the same way to the
non-thermal desorption mechanisms, and the sensitivity also depends on the
physical conditions. Thus, it is mandatory to include all of them. Chemical
desorption seems to be essential in reproducing the observations for H
densities smaller than $4\times 10^4$~cm$^{-3}$, whereas sputtering is
essential above this density. The models are, however, systematically below the
observed methanol abundances. A more efficient chemical desorption and a more
efficient sputtering could better reproduce the observations. In conclusion,
the sputtering of ices by cosmic-rays collisions may be the most efficient
desorption mechanism at high density (a few $10^4$~cm$^{-3}$ under the
conditions studied here) in cold cores, whereas chemical desorption is still
required at smaller densities. Additional works are needed on both mechanisms
to assess their efficiency with respect to the main ice composition.
