Cosmic ray sputtering yield of interstellar ice mantles

E Dartois,H Rothard,M Chabot,B Augé,T Id Barkach,P Boduch,A N Agnihotri

doi:10.1051/0004-6361/202039535

Abstract

Aims. 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. Methods. 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. Results. 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.

Highlights

In the dense and cold zones of the interstellar medium, dust grains are covered with volatile solids, which are relatively protected from ambient radiation fields outside the cloud
Model As discussed previously when modelling the evolution of water ice mantles (Dartois et al 2015) and in the modelling of a sputtering crater in the N2 ice case of Dartois et al (2020), the column density evolution of the ice molecules submitted to ion irradiation can be described, to first order and as a function of ion fluence (F) by a differential equation: dN/dF =
The sputtering cylinder is defined by a radius rs and a height d. These parameters, reported in Table. 1, are calculated from the measurement access to the more or loefssNdpraonmd iYns∞en. tTehleosnegpatairoanmoeftetrhsealsspougttievreing cylinder, which is species- and deposited-energy-dependent. To monitor this elongation within the cylinder approximation one can calculate the so-called aspect-ratio parameter

Summary

Introduction

In the dense and cold zones of the interstellar medium, dust grains are covered with volatile solids (the ice mantles), which are relatively protected from ambient radiation fields outside the cloud. 3. Model As discussed previously when modelling the evolution of water ice mantles (Dartois et al 2015) and in the modelling of a sputtering crater in the N2 ice case of Dartois et al (2020), the column density evolution of the ice molecules submitted to ion irradiation can be described, to first order and as a function of ion fluence (F) by a differential equation: dN/dF =. TTehleosnegpatairoanmoeftetrhsealsspougttievreing cylinder, which is species- and deposited-energy-dependent To monitor this elongation within the cylinder approximation one can calculate the so-called aspect-ratio parameter (heightto-diameter ratio of the cylinder in the semi-infinite ice film case).

Results and discussion

Relationship between sputtering depth and stopping power

Conclusions

Methods