Laboratory H₂O:CO₂ ice desorption: entrapment and its parameterization with an extended three-phase model

¹ Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
² Harvard-Smithsonian Center for Astrophysics, MS 42, 60 Garden Street, Cambridge, MA 02138, USA
³ Institute for Molecules and Materials, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
⁴ Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA

Abstract

Ice desorption affects the evolution of the gas-phase chemistry during the protostellar stage, and also determines the ice composition of comets forming in circumstellar disks. From observations, most volatile species, including CO₂, are found in H₂O-dominated ices. In this study, the desorption of CO₂ mixed in H₂O ice and the impact of ice thickness, mixture ratio and heating rate are experimentally determined. The results are used to parametrize an extended three-phase model (gas, ice surface and ice mantle) which describes ice mixture desorption using rate equations and a minimum number of free parameters. The model can be used to predict the evolution in thickness and concentration of volatile-rich H₂O ice during infall of icy grains around protostars.