TY - JOUR
T1 - The carriers of the interstellar unidentified infrared emission features
T2 - Aromatic or aliphatic?
AU - Li, Aigen
AU - Draine, B. T.
N1 - Copyright:
Copyright 2014 Elsevier B.V., All rights reserved.
PY - 2012/12/1
Y1 - 2012/12/1
N2 - The unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm, 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 μm and 6.85 μm 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.
AB - The unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm, 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 μm and 6.85 μm 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.
KW - ISM: lines and bands
KW - ISM: molecules
KW - dust, extinction
UR - http://www.scopus.com/inward/record.url?scp=84870224776&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84870224776&partnerID=8YFLogxK
U2 - 10.1088/2041-8205/760/2/L35
DO - 10.1088/2041-8205/760/2/L35
M3 - Article
AN - SCOPUS:84870224776
VL - 760
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
SN - 2041-8205
IS - 2
M1 - L35
ER -