The Infrared Spectra of Very Large, Compact, Highly Symmetric, Polycyclic Aromatic Hydrocarbons (PAHs)
By C. Bauschlicher, Jr., E. Peeters, L. Allamandola. 2008
166 citations recorded by the source corpus.
The mid-infrared spectra of large PAHs ranging from C54H18 to C130H28 are determined computationally using density functional theory. Trends in the band positions and intensities as a function of PAH size, charge, and geometry are discussed. Regarding the 3.3, 6.3, and 11.2 μm bands similar conclusions hold as with small PAHs. This does not hold for the other features. The larger PAH cations and anions produce bands at 7.8 μm and, as PAH sizes increases, a band near 8.5 μm becomes prominent and shifts slightly to the red. In addition, the average anion peak falls slightly to the red of the average cation peak. The similarity in behavior of the 7.8 and 8.6 μm bands with the astronomical observations suggests that they arise from large, cationic and anionic PAHs, with the specific peak position and profile reflecting the PAH cation to anion concentration ratio and relative intensities of PAH size. Hence, the broad astronomical 7.7 μm band is produced by a mixture of small and large PAH cations and anions, with small and large PAHs contributing more to the 7.6 and 7.8 μm components, respectively. For the CH out-of-plane vibrations, the duo hydrogens couple with the solo vibrations and produce bands that fall at wavelengths slightly different than their counterparts in smaller PAHs. As a consequence, previously deduced PAH structures are altered in favor of more compact and symmetric forms. In addition, the overlap between the duo and trio bands may reproduce the blue-shaded 12.8 μm profile.
Subfields: Astronomy and Astrophysics, Organic Chemistry, Physical and Theoretical Chemistry
View Paper: https://www.semanticscholar.org/paper/c980df7eba8df806fd6b9deb4cf9b03c19bb5e28
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In Astronomy and Astrophysics
Citations in the corpus
- THE NASA AMES POLYCYCLIC AROMATIC HYDROCARBON INFRARED SPECTROSCOPIC DATABASE: THE COMPUTED SPECTRA (2010, unknown): “…of the PAH carriers (e.g., Joblin et al. 1994; Li & Draine 2001; Hony et al. 2001; Peeters et al. 2002; van Diedenhoven et al. 2004; Mulas et al. 2006; Bauschlicher et al. 2008, 2009; Galliano et al. 2008; Boersma et al. 2009, 2010; Mattioda et al. 2009; Ricca et al. 2010, and references therein).”
- THE INFRARED SPECTRA OF VERY LARGE IRREGULAR POLYCYCLIC AROMATIC HYDROCARBONS (PAHs): OBSERVATIONAL PROBES OF ASTRONOMICAL PAH GEOMETRY, SIZE, AND CHARGE (2009, background): “Table 1 shows that the non-bay CH band in the cations falls between 3.249 and 3.259 μm, compared with the range of 3.252–3.257 μm for the comparably sized PAHs (C78H22– C130H28) discussed in Paper I.”