Hexa-peri-benzocoronene, a candidate for the origin of the diffuse interstellar visible absorption bands ?

Hendel, W.; Khan, Zahid H.; Schmidt, Werner

doi:10.1016/s0040-4020(01)87517-7

Cited by 86 publications

(71 citation statements)

References 17 publications

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“…4, dotted line) similar to those of symmetric, alkyl substituted hexabenzocoronene (HBC). 5 These correspond to the b and p absorption bands generally observed for HBCs. 6 In addition longer wavelength absorptions with l max 408 and 432 nm are seen; these p -p* transitions are usually symmetry forbidden in all carbon HBC but appear in 2 due to its lower symmetry.…”

supporting

confidence: 52%

Thienyl directed polyaromatic C–C bond fusions: S-doped hexabenzocoronenes

et al. 2011

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supporting

confidence: 52%

Thienyl directed polyaromatic C–C bond fusions: S-doped hexabenzocoronenes

et al. 2011

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“…1. Calibrated solution spectra obtained in the nonpolar solvent cyclohexane for anthracene, phenanthrene, pyrene, and benzo[ghi]perylene (Karcher et al 1985) and in 1,2,4-trichlorobenzene for hexabenzocoronene (Hendel et al 1986) are used as references for the determination of absolute absorption cross sections as described in the next section. The solution spectrum of 2,3-benzofluorene has been measured in our laboratory, using cyclohexane as solvent.…”

Section: Laboratory Datamentioning

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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“…In the present paper we use the CTOCD-DZ distributed-origin, ab initio method [8] (see Computational Methods for details) to visualise the current density induced by a perpendicular external magnetic field in the planar forms of circumcoronene (1, C 54 H 18 ) and two derivatives that can be formally derived from it by removal of boundary hexagons, planar hexabenzo[bc,ef,hi,kl,no,qr]coronene (2 a, C 42 H 18 ) [9] and hexabenzo[a,d,g,j,m,p]coronene (3 a, C 48 H 24 ) (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Perimeter Effects on Ring Currents in Polycyclic Aromatic Hydrocarbons: Circumcoronene and Two Hexabenzocoronenes

Soncini

Steiner

Fowler

et al. 2003

Chemistry A European J

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Current-density maps are calculated at an ab initio level for the three symmetrical polycyclic aromatic hydrocarbons, circumcoronene [1 (D 6h )], hexabenzo [bc,ef,hi,kl,no,qr] D 6h ) and 2 b (D 3d )], and hexabenzo [a,d,g,j,m,p] D 6 ) and 3 c (D 3d )], all of which can be formally derived by annelation of benzene rings to a coronene core. Whilst 1 is planar, 2 has a non-planar minimum that is effectively isoenergetic with its planar form, and 3 has a well defined nonplanar structure. The shape of the molecular boundary rather than the planarity of the molecule plays the critical ro √ le in the character of the predicted currents. Formal deletion of outer hexagons from circumcoronene (1) in two different ways produces either hexabenzocoronene 2 with a prediction of disjoint local benzenoid diatropic currents linked by a global perimeter, or 3 with a giant diatropic perimeter current enclosing a weak paramagnetic circulation on the central hexagon. The current density map of 1 is effectively a superposition of those of 2 and 3. Its strong diatropic perimeter current subsumes the six weaker diatropic benzenoid circulations evident in 2, and bifurcates in the six outer benzenoid rings that form the corners of the giant hexagon; its benzene ™hub∫ sustains a diatropic current, as would be expected from the partial cancellation of the strong diatropic hub current of 2 by the weaker paratropic hub current of 3. The relationship between the three molecules is rationalised by considering orbital contributions to their current density maps.coronene [2 a (

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Hexa-peri-benzocoronene, a candidate for the origin of the diffuse interstellar visible absorption bands ?

Cited by 86 publications

References 17 publications

Thienyl directed polyaromatic C–C bond fusions: S-doped hexabenzocoronenes

Thienyl directed polyaromatic C–C bond fusions: S-doped hexabenzocoronenes

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

Perimeter Effects on Ring Currents in Polycyclic Aromatic Hydrocarbons: Circumcoronene and Two Hexabenzocoronenes

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