On the origin of the 11.3 micron unidentified infrared emission feature

Abstract

The 11.3 $\mu$m emission feature is a prominent member of the family of unidentified infrared emission (UIE) bands and is frequently attributed to out-of-plane bending modes of polycyclic aromatic hydrocarbon (PAH) molecules. We have performed quantum mechanical calculations of 60 neutral PAH molecules and found that it is difficult to reconcile the observed astronomical feature with any or a mix of these PAH molecules. We have further analyzed the fitting of spectra of several astronomical objects by the NASA PAH database program and found that reasonable fittings to the observed spectra are only possible by including significant contributions from oxygen and/or magnesium containing molecules in the mix. A mixed of pure PAH molecules, even including units of different sizes, geometry and charged states, is unable to fit the astronomical spectra. Preliminary theoretical results on the vibrational spectra of simple molecules with mixed aromatic/aliphatic structures show that these structures have consistent bundles of vibrational modes and could be viable carriers of the UIE bands.

28 pages, 11 figures, accepted for publication in ApJ

References in corpus (6)

• Variations of the Mid-IR Aromatic Features Inside and Among Galaxies
• On-line database of the spectral properties of polycyclic aromatic hydrocarbons
• On the viability of the PAH model as an explanation of the unidentified infrared emission features
• Characterizing the infrared spectra of small, neutral, fully dehydrogenated PAHs
• The 11.2 $\mu$m emission of PAHs in astrophysical objects
• A Theoretical Study on the Vibrational Spectra of PAH Molecules with Aliphatic Sidegroups

Cited by in corpus (3)

• A Small Fullerene (C24) may be the Carrier of the 11.2 micron Unidentified Infrared Band
• On the Origin of the 3.3 Micron Unidentified Infrared Emission Feature
• The 6 $\mu$m Feature as A Tracer of Aliphatic Components of Interstellar Carbonaceous Grains