On-line database of the spectral properties of polycyclic aromatic hydrocarbons

Malloci, Giuliano; Joblin, C.; Mulas, G.

doi:10.1016/j.chemphys.2007.01.001

Cited by 197 publications

(243 citation statements)

References 119 publications

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“…For the other PAHs discussed in this paper, absorption cross sections of calculated spectra are available in a database (Malloci et al 2004(Malloci et al , 2007. Unfortunately, the theoretical spectra were convoluted with a too broad line shape function making a comparison with our experimental data very difficult or even impossible.…”

Section: Determination Of Absolute Absorption Cross Sections For Supementioning

confidence: 99%

Abundances of PAHs in the ISM: confronting observations with experimental results

Gredel

Carpentier

Rouillé

et al. 2011

A&A

104

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Context. The identification of the carriers of the diffuse interstellar bands (DIBs) is the longest standing problem in the study of the interstellar medium. Here we present recent UV laboratory spectra of various polycyclic aromatic hydrocarbons (PAHs) and explore the potential of these molecules as carriers of the DIBs. Whereas, in the near IR range, the PAHs exhibit vibrational bands that are not molecule-specific, their electronic transitions occurring in the UV/vis provide characteristic fingerprints. The comparison of laboratory spectra calibrated in intensity with high signal-to-noise observational data in the UV enables us to establish new constraints on PAH abundances. Aims. From a detailed comparison of the gas-phase and Ne-matrix absorption spectra of anthracene, phenanthrene, pyrene, 2,3-benzofluorene, benzo[ghi]perylene, and hexabenzocoronene with new interstellar spectra, we aim to infer the abundance of these PAHs in the interstellar medium. Methods. We present spectra of PAHs measured at low temperature in the gas phase and in an Ne matrix, and present methods to derive absolute absorption cross sections for the matrix and gas phase spectra. We have obtained high signal to noise (S/N > 100) absorption spectra toward five lines of sight with reddenings of E B−V = 1−1.6 mag. The spectra cover the 3050−3850 Å wavelength region where the PAHs studied here show prominent absorption features. Results. From the observations, we infer upper limits in the fractional abundances of the PAHs studied here. Upper limits in the column densities of anthracene of 0.8−2.8 × 10 12 cm −2 and of pyrene and 2,3-benzofluorene ranging from 2−8 × 10 12 cm −2 are inferred. Upper limits in the column densities of benzo [ghi]perylene are 0.9−2.4 × 10 13 and 10 14 cm −2 for phenanthrene. The measurements indicate fractional abundances of anthracene, pyrene, and 2,3-benzofluorene of a few times 10 −10 . Upper limits in the fractional abundance of benzo [ghi]perylene of a few times 10 −9 and of phenanthrene of few times 10 −8 are inferred. Toward CPD −32 • 1734, we found near 3584 Å an absorption line of OH + , which was discovered in the interstellar medium only very recently. Conclusions. The fractional abundances of PAHs inferred here are up to two orders of magnitude lower than estimated total PAH abundances in the interstellar medium. This indicates that either neutral PAHs are not abundant in translucent molecular clouds or that a PAH population with a wide variety of molecules is present.

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Section: Determination Of Absolute Absorption Cross Sections For Supementioning

confidence: 99%

Abundances of PAHs in the ISM: confronting observations with experimental results

Gredel

Carpentier

Rouillé

et al. 2011

A&A

104

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“…This approach is however degenerate, given the fact that the band ratios depend on size, ionization and hydrogenation states. Recently, Draine & Li (2007) (hereafter DL07) added the constraints provided by the extensive theoretical database of Malloci et al (2007) to define a new set of band parameters, both for neutral and cationic PAHs. Here we use the cross-sections defined in DL07 with the following modifications.…”

Section: Appendix A: Dust Propertiesmentioning

confidence: 99%

The global dust SED: tracing the nature and evolution of dust with DustEM

Compiègne

Verstraete

Jones

et al. 2010

A&A

404

724

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The Planck and Herschel missions are currently measuring the far-infrared to millimeter emission of dust, which combined with existing IR data, will for the first time provide the full spectral energy distribution (SED) of the galactic interstellar medium dust emission, from the mid-IR to the mm range, with an unprecedented sensitivity and down to spatial scales ∼30 . Such a global SED will allow a systematic study of the dust evolution processes (e.g. grain growth or fragmentation) that directly affect the SED because they redistribute the dust mass among the observed grain sizes. The dust SED is also affected by variations of the radiation field intensity. Here we present a versatile numerical tool, DustEM, that predicts the emission and extinction of dust grains given their size distribution and their optical and thermal properties. In order to model dust evolution, DustEM has been designed to deal with a variety of grain types, structures and size distributions and to be able to easily include new dust physics. We use DustEM to model the dust SED and extinction in the diffuse interstellar medium at high-galactic latitude (DHGL), a natural reference SED that will allow us to study dust evolution. We present a coherent set of observations for the DHGL SED, which has been obtained by correlating the IR and HI-21 cm data. The dust components in our DHGL model are (i) polycyclic aromatic hydrocarbons; (ii) amorphous carbon and (iii) amorphous silicates. We use amorphous carbon dust, rather than graphite, because it better explains the observed high abundances of gas-phase carbon in shocked regions of the interstellar medium. Using the DustEM model, we illustrate how, in the optically thin limit, the IRAS/Planck HFI (and likewise Spitzer/Herschel for smaller spatial scales) photometric band ratios of the dust SED can disentangle the influence of the exciting radiation field intensity and constrain the abundance of small grains (a < ∼ 10 nm) relative to the larger grains. We also discuss the contributions of the different grain populations to the IRAS, Planck (and similarly to Herschel) channels. Such information is required to enable a study of the evolution of dust as well as to systematically extract the dust thermal emission from CMB data and to analyze the emission in the Planck polarized channels. The DustEM code described in this paper is publically available.

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“…Nevertheless, as inferred from the aromatic infrared emission bands, the bulk of interstellar PAHs are probably larger than the species we studied here ( > ∼ 40 C atoms; Tielens 2008). The first electronic transitions of these larger molecules are generally located at wavelengths longer than ≈400 nm (see, e.g., Ruiterkamp et al 2002;Malloci et al 2007). At shorter wavelengths, the bandwidths are usually governed by the short lifetimes of the excited (high-energy) states and by vibrational interactions with energetically lowerlying states (Rouillé et al 2009), i.e., they should be very similar for completely free and matrix-isolated molecules (Steglich et al 2011).…”

Section: Astrophysical Implications -Extension To Larger Species In Tmentioning

confidence: 99%

The smoothness of the interstellar extinction curve in the UV

Steglich

Carpentier

Jäger

et al. 2012

A&A

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Context. As revealed by high-resolution spectral investigations in the wavelength range between 300 and 400 nm, the interstellar extinction curve does not display any of the sharp electronic absorption bands that are characteristic for large polyatomic molecules, such as polycyclic aromatic hydrocarbons (PAHs), which belong to the most abundant interstellar molecules. Aims. We aim to verify whether the absorption curves of mixtures of medium-sized PAHs produced in the laboratory can explain the astronomical observations. Methods. The PAH mixtures were synthesized by infrared laser pyrolysis and subsequent chemical extraction and size separation. The matrix isolation technique was used to study the absorption spectra of isolated molecules at low temperature. Results. Our experimental results demonstrate that the UV-visible absorption curves of PAH mixtures can be very smooth, displaying no sharp bands, if the molecular diversity is sufficiently high. Conclusions. In view of the absence of sharp electronic features on the interstellar extinction curve for 300 < λ < 400 nm, we conclude from our experimental findings that the interstellar PAH population must be very diverse. The low fractional abundances of individual species prevent their detection on the basis of spectral fingerprints in the UV.

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On-line database of the spectral properties of polycyclic aromatic hydrocarbons

Cited by 197 publications

References 119 publications

Abundances of PAHs in the ISM: confronting observations with experimental results

Abundances of PAHs in the ISM: confronting observations with experimental results

The global dust SED: tracing the nature and evolution of dust with DustEM

The smoothness of the interstellar extinction curve in the UV

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