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Issue A&A
Volume 456, Number 1, September II 2006
Page(s) 161 - 169
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20065435



A&A 456, 161-169 (2006)
DOI: 10.1051/0004-6361:20065435

Diagnostics for specific PAHs in the far-IR: searching neutral naphthalene and anthracene in the Red Rectangle

G. Mulas1, 2, G. Malloci2, C. Joblin2 and D. Toublanc2

1  INAF - Osservatorio Astronomico di Cagliari - Astrochemistry Group, Strada 54, Loc. Poggio dei Pini, 09012 Capoterra (CA), Italy
    e-mail: gmulas@ca.astro.it
2  Centre d'Étude Spatiale des Rayonnements, CNRS et Université Paul Sabatier-Toulouse 3, Observatoire Midi-Pyrénées, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 04, France
    e-mail: [giuliano.malloci;christine.joblin;dominique.toublanc]@cesr.fr

(Received 13 April 2006 / Accepted 17 May 2006 )

Abstract
Context.In the framework of the interstellar polycyclic aromatic hydrocarbons (PAHs) hypothesis, far-IR skeletal bands are expected to be the fingerprints of single species in this class.
Aims.We address the question of detectability of low energy PAH vibrational bands, with respect to spectral contrast and intensity ratio with "classical" Aromatic Infrared Bands (AIBs).
Methods.We extend our established Monte Carlo model of the photophysics of specific PAHs in astronomical environments to include rotational and anharmonic band structure. The required molecular parameters were calculated in the framework of the Density Functional Theory.
Results.We calculate the detailed spectral profiles of three low-energy vibrational bands of neutral naphthalene and four low-energy vibrational bands of neutral anthracene. They are used to establish detectability constraints based on intensity ratios with "classical" AIBs. A general procedure is suggested to select promising diagnostics and tested on available Infrared Space Observatory data for the Red Rectangle nebula.
Conclusions.The search for single, specific PAHs in the far-IR is a challenging, but promising task, especially in view of the forthcoming launch of the Herschel Space Observatory.


Key words: astrochemistry -- line: identification -- molecular processes -- ISM: individual objects: Red Rectangle -- ISM: lines and bands -- ISM: molecules



© ESO 2006


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