Simulation of the Formation and Morphology of Ice Mantles on Interstellar Grains

Abstract

Although still poorly understood, the chemistry that occurs on the surfaces of interstellar dust particles profoundly affects the growth of molecules in theinterstellar medium.An important setof surface reactions producesicymantles of manymonolayers in cold and dense regions. Themonolayersare dominated bywater ice,but alsocontain CO, CO2, and occasionally methanol, as well as minor constituents. In this paper, the rate of production of water-ice-dominated mantles is calculated for different physical conditions of interstellar clouds and for the first time images of the morphology of interstellar ices are presented. For this purpose, the continuous-time random-walk Monte Carlo simulation technique has been used. The visual extinction, density, and gas and grain temperatures are varied. It is shown that our stochastic approach can reproduce the important observation that ice mantles only grow in the denser regions.