A New Model for Cosmic‐Ray Ion Erosion of Volatiles from Grains in the Interstellar Medium

Erosion of small grains or grain mantles is important in a number of astrophysical environments. Since energy deposition events produced by energetic ions can create a "hot" region in a grain, simple thermal spike models have been applied to estimate the sputtering efficiency. Here the results of molecular dynamics (MD) simulations are used to describe sputtering from the "heat spike" formed by a heavy cosmic-ray (CR) ion. These results are compared to extrapolations of laboratory sputtering data for frozen volatiles and to earlier models for CR ion-induced desorption. The CO and H 2 O desorption rates for thick mantles or for whole volatile grains are given and are found to disagree with results obtained using heat spike models. Further, the rates are an order of magnitude smaller and an order of magnitude larger, respectively, than the rates typically used for desorption of CO and H 2 O from a thin mantle on a 0.1 μm silicate core in a molecular cloud. The model given here can now be used for calculating energetic ion-induced desorption from grains in a variety of astrophysical environments and of other compositions and sizes.