EDP Sciences
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Volume 415, Number 1, February III 2004
Page(s) 203 - 215
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20031669

A&A 415, 203-215 (2004)
DOI: 10.1051/0004-6361:20031669

Cosmic ray induced explosive chemical desorption in dense clouds

C. J. Shen, J. M. Greenberg, W. A. Schutte and E. F. van Dishoeck

Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
(Received 3 January 2003 / Accepted 29 October 2003 )

The desorption due to the energy release of free radicals in the ice mantles of a dust grain is investigated theoretically by calculating the ultraviolet radiation field inside the cloud, the free radical accumulation, the cosmic-ray heating of the grain and then the desorption in this situation starting from the cosmic-ray energy spectra. This model can reproduce the observations of the CO gas abundances and level of depletion in dark clouds such as L977 and IC 5146 with a combination of input parameters which are either constrained by independent observations or have been derived independently from laboratory experiments. We investigate other desorption mechanisms and conclude that they cannot explain the observations. The model also shows that the energy input by the cosmic-ray induced ultraviolet field is almost one order of magnitude larger than the direct energy input by cosmic-ray particles. This strengthens the conclusion that desorption due to the energy release by ultraviolet photon produced radicals dominates over direct cosmic-ray desorption.

Key words: ISM: dust, extinction -- ISM: cosmic rays -- ISM: clouds -- ISM: individual: objects: L977, IC 5146

Offprint request: E. F. van Dishoeck, ewine@strw.leidenuniv.nl

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