PAHs as the carriers of the 3.3 and 3.4 μm emission bands

Joblin, C.; Tielens, A. G. G. M.; Allamandola, L. J.; Léger, Alain; D’Hendecourt, L.; Geballe, T. R.; Boissel, P.

doi:10.1016/0032-0633(95)00022-w

Cited by 103 publications

(227 citation statements)

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“…This is illustrated in Figure 4 which shows a comparison between the emission from the ionized ridge in the Orion Nebula and the composite absorption spectrum generated by coaddition of 11 PAH spectra, judiciously chosen from the laboratory database (See [97] for a discussion of the fitting procedure). Note that since the expected matrix shift (5-10 cm -1 ) and vibrational excitation red-shift between absorption and emission band positions (5-15 cm -1 , [52]) are significantly smaller than the 30 cm -1 natural linewidth expected from the interstellar emitters, these effects have not been compensated for in the figure.…”

Section: Interstellar Pahs: Mid-infrared Spectral Propertiesmentioning

confidence: 99%

“…Indeed, in this manner it has been possible to measure the absorption and emission spectra of a few species and these studies have produced important insights into the astrophysical problem. [48][49][50][51][52] Nevertheless, this technique faces a number of serious practical difficulties for all but the very smallest PAHs. Moreover, these difficulties become increasingly problematic as molecular size increases and the volatility of the sample decreases.…”

Section: Interstellar Pahs: the Laboratory Challengementioning

confidence: 99%

“…[111]), ionization produces some notable changes in region boundaries. Considering these modified domains and taking into account the roughly 0.1 µm red-shift in the peak position for PAHs emitting at temperatures of 500 -1000 K [49,50,52,60] we are left with the following conclusions:…”

Section: The 15 To 20 µM Emission Plateau and A New Emission Band At mentioning

confidence: 99%

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From Interstellar Polycyclic Aromatic Hydrocarbons and Ice to Astrobiology

Allamandola

Hudgins

2003

Solid State Astrochemistry

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Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon rich molecules widespread throughout the interstellar medium (ISM) considered impossible.Today the composition of dust in the diffuse ISM is reasonably well constrained to micron-sized cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. In dense molecular clouds, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose major components are is very well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by earlier interstellar chemistry standards, is widespread throughout the Universe. This paper presents a detailed summary of these disparate interstellar components and ends by considering both of them as important feedstock to the chemical inventory of the primordial Earth. Particular attention is paid to their possible role in the chemistry that led to the origin of life. An extensive reference list is given to allow the student entry into the full depth of the literature.The first part of this paper focuses on interstellar PAHs. The laboratory and theoretical underpinning which supports the PAH model is reviewed in some detail. This is followed by a few specific examples which demonstrate how these data can be used to analyze the interstellar spectra and probe local conditions in different emission zones. These examples include tracing the evolution of carbon as it passes from its birthsite in circumstellar shells through the ISM, determining specifics about the cosmic PAH population in many different environments including PAH size and structure, and probing local conditions in the different emission zones.The second part of this paper summarizes the laboratory and observational background leading to our current understanding of interstellar/precometary ices. Although the most abundant interstellar ice components are the very simple molecules such as H 2 O, CH 3 OH, CO, CO 2 , and NH 3 , more complex species including accreted PAHs and those formed by UV and cosmic ray processing within the ice must also be present. Here we give a detailed summary of the photochemical evolution on those ices 2 found in the densest regions of molecular clouds, the regions where stars and planetary systems are formed. Ultraviolet photolysis of these ices produces a host of new compounds, some of which show intriguing prebiotic behavior.The last part of this paper draws all this information together and considers the possible roles these compounds might have played in early Earth...

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Section: Interstellar Pahs: Mid-infrared Spectral Propertiesmentioning

confidence: 99%

Section: Interstellar Pahs: the Laboratory Challengementioning

confidence: 99%

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From Interstellar Polycyclic Aromatic Hydrocarbons and Ice to Astrobiology

Allamandola

Hudgins

2003

Solid State Astrochemistry

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“…This study indicated that while gas-phase and matrix isolated band positions reproduce to within about 1%, band intensities can change by up to a factor of five. While the high temperatures needed to vaporize the molecules lead to substantially larger bandwidths and may appear to be astrophysically unrealistic, interstellar emission occurs from excited PAH molecules which are estimated to possess vibrational temperatures on the order of 1000 K (Joblin et al 1995). Moreover, spectra recorded at different temperatures of the oven yield direct information on the anharmonic frequency shifts of vibrational bands (Pirali et al 2009), which are important in modelling IR emission spectra (Cook & Saykally 1998) and which are hard to estimate computationally for large systems.…”

Section: Gas-phase Absorption Spectroscopymentioning

confidence: 99%

Laboratory infrared spectroscopy of PAHs

Oomens

2011

EAS Publications Series

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“…These emission features are indicative of the presence of aromatic hydrocarbons (Duley & Williams 1981, Leger & Puget 1984, Allamandola et al 1989) and other bands, notably those in the 3.4-3.6 µm range, are characteristic of CH vibrations in sp 3 -hybridized bonded hydrocarbons (Duley & Williams 1983). However, the composition of the compounds responsible for these bands is still uncertain despite numerous theoretical and laboratory studies (Scott et al 1997, Hudgins et al 1999, 2004, van Diedenhoven et al 2004).…”

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confidence: 99%

Simulation of organic interstellar dust in the laboratory

Duley

2008

Proc. IAU

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Abstract. New techniques for the generation and analysis of carbon nanoparticles (CNPs) have been developed and have resulted in the production of CNP samples whose infrared spectral properties are essentially identical to those observed in interstellar absorption and emission. These particles are of mixed aromatic/aliphatic composition. Spectra of CNPs containing 10 2 -10 4 atoms will be discussed in relation to spectra of interstellar materials. We find that infrared line widths in these samples are typically 10-30 cm −1 , but can be as small as 2 cm −1 . Simulation of the 3.28 µm feature is shown to yield important new insight into the nature of interstellar CNPs.

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PAHs as the carriers of the 3.3 and 3.4 μm emission bands

Cited by 103 publications

References 13 publications

From Interstellar Polycyclic Aromatic Hydrocarbons and Ice to Astrobiology

From Interstellar Polycyclic Aromatic Hydrocarbons and Ice to Astrobiology

Laboratory infrared spectroscopy of PAHs

Simulation of organic interstellar dust in the laboratory

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