Desorption of CO and O2 interstellar ice analogs

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Acharyya, K. and Fuchs, G.W. and Fraser, H.J. and van Dishoeck, E.F. and Linnartz, H. (2007) Desorption of CO and O2 interstellar ice analogs. Astronomy and Astrophysics, 466 (3). pp. 1005-1012. ISSN 0004-6361 (https://doi.org/10.1051/0004-6361:20066272)

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Abstract

Solid O2 has been proposed as a possible reservoir for molecular oxygen in dense clouds through freeze-out processes. The aim of this work is to characterize quantitatively the physical processes that are involved in the desorption kinetics of CO-O2 ices by interpreting laboratory temperature programmed desorption (TPD) data. This information is used to simulate the behavior of CO-O2 ices under astrophysical conditions. The TPD spectra have been recorded under ultra high vacuum conditions for pure, layered and mixed morphologies for different thicknesses, temperatures and mixing ratios. An empirical kinetic model is used to interpret the results and to provide input parameters for astrophysical models. Binding energies are determined for different ice morphologies. Independent of the ice morphology, the desorption of O2 is found to follow 0-order kinetics. Binding energies and temperature-dependent sticking probabilities for CO-CO, O2-O2 and CO-O2 are determined. O2 is slightly less volatile than CO, with a binding energy of versus K for pure ices. In mixed and layered ices, CO does not co-desorb with O2 but its binding energy is slightly increased compared to pure ice whereas that of O2 is slightly decreased. Lower limits to the sticking probabilities of CO and O2 are 0.9 and 0.85, respectively, at temperatures below 20 K. The balance between accretion and desorption is studied for O2 and CO in astrophysically relevant scenarios. Only minor differences are found between the two species, i.e., both desorb between 16 and 18 K in typical environments around young stars. Thus, clouds with significant abundances of gaseous CO are unlikely to have large amounts of solid O2.

  • Item type:Article
    ID code:6183
    Dates:
    Date
    Event
    May 2007
    Published
    Subjects:Science > Astronomy
    Department:Faculty of Science > Physics
    Depositing user: Miss Darcy Spiller
    Date deposited:02 Jun 2008
    Last modified:12 Dec 2024 02:14
    URI:https://strathprints.strath.ac.uk/id/eprint/6183
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