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Carbon chain abundance in the diffuse interstellar mediumThanks to the mid-IR sensitivities of the ISO and IRTS orbiting spectrometers it is now possible to search the diffuse interstellar medium for heretofore inaccessible molecular emission. In view of the recent strong case for the presence of C(7-) (Kirkwood et al. 1998, Tulej et al. 1998),and the fact that carbon chains possess prominent infrared active modes in a very clean portion of the interstellar spectrum, we have analyzed the IRTS spectrum of the diffuse interstellar medium for the infrared signatures of these species. Theoretical and experimental infrared band frequencies and absolute intensities of many different carbon chain species are presented. These include cyanopolyynes, neutral and anionic linear carbon molecules, and neutral and ionized, even-numbered, hydrogenated carbon chains. We show that--as a family--these species have abundances in the diffuse ISM on the order of 10(-10) with respect to hydrogen, values consistent with their abundances in dense molecular clouds. Assuming an average length of 10 C atoms per C-chain implies that roughly a millionth of the cosmically available carbon is in the form of carbon chains and that carbon chains can account for a few percent of the visible to near-IR diffuse interstellar band (DIB) total equivalent width (not DIB number).
Document ID
20040088876
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Allamandola, L. J.
(NASA Ames Research Center Moffett Field CA United States)
Hudgins, D. M.
Bauschlicher, C. W. Jr
Langhoff, S. R.
Date Acquired
August 21, 2013
Publication Date
December 10, 1999
Publication Information
Publication: Astronomy and astrophysics
Volume: 352
Issue: 2
ISSN: 0004-6361
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other

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