Modeling the interstellar aromatic infrared bands with co-added spectra of PAHs

Abstract

The observed variations in profiles of the interstellar aromatic infrared bands correlate with the object type and are indicative of PAH populations existing i n different sources. Spectroscopic studies on PAHs can provide tools for the int erpretation of variations accompanying the AIBs. As the observed spectra results from a mix of possible species in the region attempt is made to model this comp osite spectra by co-adding emissions from PAHs in different size groups. Theoretical IR data of PAHs having 10 to 96 carbon atoms is used to obtain emis sion spectra. The models are taken in size groups making up of small, medium and large PAHs. The models show good profile match with observations for the 7.7 $\mu m$ complex having sub-features at 7.6 and 7.8 $\mu m$. The 7.6 $\mu m$ sub-feature dominates in the spectra of medium sized PAH cations matching observations from UV rich interstellar environments. The 7.8 $\mu m$ component is more intense in the spectra of large PAH cations (model III) correlating with observations from benign astrophysical regions. A possible interpretation for the observations of $C-H$ out-of-plane bend modes and the weak outliers on the blue side of the intense 11.2 $\mu m$ band is proposed. The models provide pointers to possible PAH populations in different regions.

arXiv commentaccepted for publication in A&A

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• Spatial distribution and interpretation of the 3.3 \mum PAH emission band of the Red Rectangle
• The 11.2 $\mu$m emission of PAHs in astrophysical objects
• Laboratory gas-phase infrared spectra of two astronomically relevant PAH cations: diindenoperylene, C${}_{32}$H${}_{16}$${}^{+}$ and dicoronylene, C${}_{48}$H${}_{20}$${}^{+}$
• DFT study on interstellar PAH molecules with aliphatic side groups
• Theoretical study of infrared spectra of interstellar PAH molecules with N, NH & NH${}_2$ incorporation
• Study of vibrational spectra of polycyclic aromatic hydrocarbons with phenyl side group
• Mid-infrared vibrational study of deuterium-containing PAH variants
• Experimental and theoretical study on the infrared spectroscopy of astrophysically relevant PAH derivatives 2- and 9-vinylanthracene
• PAH and nbL Features Detection in Planetary Nebulae NGC 7027 and BD +303639 with TIRCAM2 Instrument on 3.6m DOT
• Vibrational dynamics of phenylphenanthrenes with phenyl group at different positions
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