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

Journal Article · Sat Dec 01 04:00:00 EST 2012 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/760/2/L35· OSTI ID:22078398

Aigen, Li ^[1]

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1. Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States)

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.

• OSTI ID: 22078398
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 760; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CARBON
CARRIERS
COAL
HYPOTHESIS
INFRARED RADIATION
KEROGEN
NANOSTRUCTURES
PARTICLES
PHOTON EMISSION
POLYCYCLIC AROMATIC HYDROCARBONS
VIBRATIONAL STATES