2008ApJ...678..316B


C.D.S. - SIMBAD4 rel 1.7 - 2021.05.05CEST23:23:16

2008ApJ...678..316B - Astrophys. J., 678, 316-327 (2008/May-1)

The infrared spectra of very large, compact, highly symmetric, polycyclic aromatic hydrocarbons (PAHs).

BAUSCHLICHER C.W.Jr, PEETERS E. and ALLAMANDOLA L.J.

Abstract (from CDS):

The mid-infrared spectra of large PAHs ranging from C54H18 to C130H_ 28_ 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.

Abstract Copyright:

Journal keyword(s): Astrochemistry - Infrared: ISM - ISM: Lines and Bands - ISM: Molecules - Line: Identification - Molecular Data - Techniques: Spectroscopic

Simbad objects: 8

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Number of rows : 8

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 NGC 2023 RNe 05 41 37.9 -02 15 52           ~ 581 1
2 HD 44179 pA* 06 19 58.2185496 -10 38 14.706068 9.51 9.33 9.02     B9Ib/II 725 0
3 PN Vo 1 PN 06 59 26.4078328215 -79 38 47.129323563   16.7 15.8     [WC10] 94 0
4 EM* MWC 922 Be* 18 21 16.059408 -13 01 25.68432     13.80 13.65   B[e] 85 0
5 [WAM82] 023.955+0.152 HII 18 34 24.9 -07 54 50           ~ 70 1
6 NGC 7027 PN 21 07 01.571952 +42 14 10.47120   10.358 8.831 10.157   ~ 2357 1
7 IRAS 21190+5140 HII 21 20 44.8 +51 53 28           ~ 128 2
8 SH 2-159 Y*O 23 15 31.27440 +61 07 10.4450           ~ 176 2

    Equat.    Gal    SGal    Ecl

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2021.05.05-23:23:16

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