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Photodesorption of ices – Releasing organic precursors into the gas phase

Published online by Cambridge University Press:  01 February 2008

Karin I. Öberg ,
Ewine F. van Dishoeck  and
Harold Linnartz
Karin I. Öberg
Affiliation:
Raymond and Beverly Sackler Laboratory for AstrophysicsLeiden Observatory, Leiden UniversityP.O. Box 9513, NL–2300 RA Leiden, the Netherlands email: [email protected], [email protected]
Ewine F. van Dishoeck
Affiliation:
Leiden Observatory, Leiden UniversityP.O. Box 9513, NL–2300 RA Leiden, the Netherlands email: [email protected]
Harold Linnartz
Affiliation:
Raymond and Beverly Sackler Laboratory for AstrophysicsLeiden Observatory, Leiden UniversityP.O. Box 9513, NL–2300 RA Leiden, the Netherlands email: [email protected], [email protected]
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Abstract

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A long-standing problem in interstellar chemistry is how molecules can be maintained in the gas phase at the extremely low temperatures in space. Photodesorption has been suggested to explain the observed cold gas in cloud cores and disk mid-planes. We are studying the UV photodesorption of ices experimentally under ultra high vacuum and at astrochemically relevant temperatures (15 – 27 K) using a hydrogen discharge lamp (7-10.5 eV). The ice desorption during irradiation is monitored using reflection absorption infrared spectroscopy and the desorbed species using mass spectrometry. We find that both the UV photodesorption rates and mechanisms are highly molecule specific. CO photodesorbs without dissocation from the surface layer of the ice. N2, which lacks dipole allowed electronic transitions in the range of the lamp, does not photodesorb. CO2 desorbs through dissociation and subsequent recombination from the top few layers of the ice. At low temperatures (15 – 18 K) the derived photodesorption rates are ~ 10−3 for CO and CO2 and < 2 × 10−4 for N2 ice per incident photon.

Keywords

Astrochemistrymolecular datamolecular processesmethods: laboratory
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 4 , Symposium S251: Organic Matter in Space , February 2008 , pp. 449 - 450
Copyright
Copyright © International Astronomical Union 2008

References

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