The adsorption and desorption of CO on and from amorphous H2O ice at astrophysically relevant temperatures has been studied using temperature programmed desorption (TPD) and reflection-absorption infrared spectroscopy (RAIRS). Solid CO is able to diffuse into the porous structure of H2O at temperatures as low as 15 K. When heated, a phase transition between two forms of amorphous H2O ice occurs over the 30-70 K temperature range, causing the partial collapse of pores and the entrapment of CO. Trapped CO is released during crystallization and desorption of the H2O film. This behavior may have a significant impact on both gas-phase and solid-phase chemistry in a variety of interstellar environments.
Collings, M. P., Dever, J. W., Fraser, H. J., McCoustra, M. R. S., & Williams, D. A. (2003). Carbon monoxide entrapment in interstellar ice analogs. Astrophysical Journal, 583, 1058-1062. https://doi.org/10.1086/345389