Volatile entrapment in amorphous water ice

Abstract

The chem. compn. of planetary bodies, including those in our own Solar System, is related to that of the icy planetesimals found in protoplanetary disks and in the earlier protostellar stages. These ices are mainly made of water mols. together with more volatiles species adsorbed onto or mixed with water ice. A key process that regulates ice chem. compn. around protostars and in disks is the ability of amorphous water ice to retain more volatile species upon warm-up. Here we quant. measure the entrapment fraction of volatile species (CO₂, H₂S, noble gases,...) from amorphous water using a combination of quartz crystal microbalance and quadrupole mass spectrometry by warming up mixed or layered ice films. Ice thickness, mixing fraction, and heating rate are varied. The particular comparison of CO₂ and H₂S entrapment in water ice highlights the role of hydrogen bonding in the underlying retention process. The quant. aspect of the exptl. work allows us to derive empirical parameters and feed them into astrochem. networks for extrapolation and assessment of volatile entrapment under astrophys. time scales.

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