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THE CARRIERS OF THE INTERSTELLAR UNIDENTIFIED INFRARED EMISSION FEATURES: AROMATIC OR ALIPHATIC?

Author(s): Li, Aigen; Draine, Bruce T.

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Abstract: The unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 mu m, commonly attributed to polycyclic aromatic hydrocarbon (PAH) molecules, have been recently ascribed to coal- or kerogen-like organic nanoparticles with a mixed aromatic-aliphatic structure. However, we show in this Letter that this hypothesis is inconsistent with observations. We estimate the aliphatic fraction of the UIE carriers based on the observed intensities of the 3.4 mu m and 6.85 mu m emission features by attributing them exclusively to aliphatic C-H stretch and aliphatic C-H deformation vibrational modes, respectively. We derive the fraction of carbon atoms in aliphatic form to be <15%. We conclude that the UIE emitters are predominantly aromatic, with aliphatic material at most a minor part of the UIE carriers. The PAH model is consistent with astronomical observations and PAHs dominate the strong UIE bands.
Publication Date: 1-Dec-2012
Electronic Publication Date: 14-Nov-2012
Citation: Li, Aigen, Draine, BT. (2012). THE CARRIERS OF THE INTERSTELLAR UNIDENTIFIED INFRARED EMISSION FEATURES: AROMATIC OR ALIPHATIC?. ASTROPHYSICAL JOURNAL LETTERS, 760 (10.1088/2041-8205/760/2/L35
DOI: doi:10.1088/2041-8205/760/2/L35
ISSN: 2041-8205
Type of Material: Journal Article
Journal/Proceeding Title: ASTROPHYSICAL JOURNAL LETTERS
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.
Notes: Supplementary data may be available at http://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2012ApJ...760L..35L



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