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
