EDP Sciences
Free access
Volume 410, Number 2, November I 2003
Page(s) 639 - 648
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20031212

A&A 410, 639-648 (2003)
DOI: 10.1051/0004-6361:20031212

Testing the "strong" PAHs hypothesis

II. A quantitative link between DIBs and far-IR emission features
G. Mulas1, G. Malloci1, 2 and P. Benvenuti2, 3

1  INAF - Osservatorio Astronomico di Cagliari - AstroChemistry Group, Strada n.54, Loc. Poggio dei Pini, 09012 Capoterra (CA), Italy
2  Dipartimento di Fisica, Università degli Studi di Cagliari, S.P. Monserrato-Sestu Km 0.7, 09042 Cagliari, Italy
3  Space Telescope-European Coordinating Facility, ESA, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Munchen, Germany

(Received 15 April 2003 / Accepted 5 August 2003)

In Paper I (Malloci et al. 2003) we proved the profile invariance of the first permitted electronic transition of the typical Polycyclic Aromatic Hydrocarbon cation C 32H 14+ as a first necessary check for the "strong" PAHs hypothesis. In this paper we derive a quantitative relation between the intensities of the former band, which ought to be observable in absorption in the visible range, and those of the far-IR bands, which are predicted by the PAH model to be simultaneously present in emission. Contrary to the mid-IR bands, collectively known as "Unidentified Infrared Bands" (UIBs), which do not discriminate specific molecules, the far IR, skeletal bands can be expected to be a fingerprint of each single species. This fact provides a number of independent constraints which must be simultaneously fulfilled for a successful PAH identification. Our approach thus offers a powerful criterion for the identification of specific PAHs, both in the presently available ISO data and in those of the forthcoming SIRTF and Herschel missions. As an interesting by-product, we quantitatively evaluate the impact of isotopic substitutions ( $\element[][13]{C}$ $\to$ $\element[][12]{C}$ and $\element[][]{D}$ $\to$ $\element[][]{H}$) on the resulting infrared emission bands.

Key words: astrochemistry -- line: identification -- molecular processes -- ISM: lines and bands -- ISM: molecules -- infrared: ISM

Offprint request: G. Mulas, gmulas@ca.astro.it

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