Processing of polycyclic aromatic hydrocarbons in evolved planetary nebulae

AbstractWe investigate the infrared emission bands from Polycyclic Aromatic Hydrocarbons (PAHs) in Galactic planetary nebulae (PNe). PAHs in PNe are assumed to be in transition from circumstellar to interstellar PAHs. We select 15 evolved PNe taking account of effective stellar temperatures and obtain infrared spectra of PNe from AKARI (2.5–5 μm) and Spitzer (5–14 μm) observations. Their evolutionary phase is estimated using [SIV]10.51/[NeII]12.81. We find that the near-infrared PAH bands are significantly enhanced along with stellar evolution sequence. We also find that the ratio of 3.4 to 3.3 μm bands is enhanced. The enhancement might indicate some chemical processing, such as hydrogenation, on small PAHs.

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Various Aspects of the Spectroscopy of PAHs (Polycyclic Aromatic Hydrocarbons)

Highlights of Astronomy ◽

10.1017/s1539299600012788 ◽

2002 ◽

Vol 12 ◽

pp. 44-47

Author(s):

Philippe Bréchignac

Keyword(s):

Polycyclic Aromatic Hydrocarbons ◽

Charge State ◽

Aromatic Hydrocarbons ◽

Near Infrared ◽

Spectroscopic Properties ◽

Infrared Emission ◽

Ir Absorption ◽

Near Ir ◽

Polycyclic Aromatic ◽

Infrared Intensities

AbstractThe exploitation of the recent observations (in particular by ISO) of the near infrared emission bands (UIBs) requires a good knowledge of the spectroscopic properties of the main proposed carriers, i.e. the Polycyclic Aromatic Hydrocarbons, which are expected to act as efficient UV/visible to infrared free-flying light converters.The charge state of the interstellar PAHs strongly affects their spectroscopy. The laboratory study of the electronic transitions of PAH cations in the gas phase enables to address important questions, like their possible contribution to the Diffuse Interstellar Bands (visible and near-IR absorption), and the mechanism responsible for electronic to vibrational intramolecular energy conversion.Microcanonical simulations based on hybrid quantum/classical theoretical methods reveal how strongly affected are the infrared intensities by both the charge state and the vibrational temperature.

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The Infrared Emission Features and Polycyclic Aromatic Hydrocarbons

Symposium - International Astronomical Union ◽

10.1017/s0074180900125161 ◽

1989 ◽

Vol 135 ◽

pp. 129-140

Author(s):

L. J. Allamandola

Keyword(s):

Polycyclic Aromatic Hydrocarbons ◽

Aromatic Hydrocarbons ◽

Related Species ◽

Infrared Emission ◽

Polycyclic Aromatic

The infrared evidence which supports the PAH hypothesis is briefly summarized. Rather than presenting a general discussion of these assignments, this paper focuses on the spectroscopic issues raised by recent observational and experimental developments. These issues include: the position and profile of the “1310” cm−1(“7.7” μm) feature, the position and intensities of the bands in the 910-710 cm−1(11-14 μm) region, the newly detected 1900 cm−1(5.3 μm) band, and the spatial and spectral variations in the 3000 cm−1(3 μm) region as well as in the 12 and 25 μm IRAS bands. It is concluded that the infrared evidence for interstellar PAHs and PAH-related species is compelling.

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