Diffusion-desorption ratio of adsorbed CO and CO 2on water ice

Abstract

Context. Diffusion of atoms and molecules is a key process for the chemical evolution in star-forming regions of the interstellar medium. Accurate data on the mobility of many important interstellar species is often not available, however, which seriously limits the reliability of models describing the physical and chemical processes in molecular clouds. Aims. Here we aim to provide the astrochemical modeling community with reliable data on the ratio between the energy barriers for diffusion and desorption for adsorbed CO and CO2on water ices. Methods. To this end, we used a fully atomistic, off-lattice kinetic Monte Carlo technique to generate dynamical trajectories of CO and CO2molecules on the surface of crystalline ice at temperatures relevant for the interstellar medium. Results. The diffusion-to-desorption barrier ratios are determined to be 0.31 for CO and 0.39 for CO2. These ratios can be directly used to improve the accuracy of current gas-grain chemical models.