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EAS Publications Series 46 (2011) 223-234
PAH-related Very Small Grains in photodissociation regions: implications from molecular simulations
Mathias Rapacioli1, Fernand Spiegelman1, Baptiste Joalland1, Aude Simon1, André Mirtschink1, Christine Joblin2, J. Montillaud2, O. Berné, D. Talbi3

The analysis of mid-IR emission suggests that a population of PAH-related very small grains containing a few hundreds of atoms are present in the deep regions of molecular clouds, although no specific species has been identified yet. In this review, we discuss several candidates for these grains: neutral and ionised PAH clusters and complexes of PAHs with Si atoms. The theoretical modelling of the properties of such molecular complexes or nanograins is a challenging task. We first present an overview of quantum chemistry derived models which can be efficiently used on-the-fly in extensive sampling of the potential energy surfaces, as required by structural optimization, classical molecular dynamics or Monte Carlo algorithms. From the simulations, various observables can be determined, such as the binding energies, finite temperature IR spectra, nucleation and evaporation rates. We discuss the relevance of those candidates in the molecular clouds photodissociation regions and propose constrains and perspectives for the nature and size of those very small grains.
1 :  LCPQ - Laboratoire de Chimie et Physique Quantiques
2 :  CESR - Centre d'étude spatiale des rayonnements
3 :  LUPM - Laboratoire Univers et Particules de Montpellier
Modélisation, Agrégats, Dynamique