Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.115c&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Astronomy and Astrophysics
Astronomy
Scientific paper
In a carbon-rich red giant or in a carbon-rich protoplanetary nebula (PPN) atmosphere, like CRL 618, the major carbon-bearing chemical species that is initially formed is acetylene.Specific chemical reactions, depending on both density and temperature conditions, could then lead to the formation of polycyclic aromatic hydrocarbons (PAHs), large aromatic planar molecules.Some of the chemical networks assume PAHs synthesis in the molecular envelops of C-rich stars, with acetylene being the major carbon source and requiring at the same time particularly dense and slow stellar winds.More in detail, the ionic chemical model involves hydrocarbon ion-neutral acetylene reactions and both hydrogenation and/or electron recombination processes, thereby implicitly accounting for the presence of low-energy electrons that we argue here to play an important role.Having found that one of the suggested intermediate species, the neutral ortho-benzyne molecule, is indeed capable of forming by electron attachment at low energy (1 eV) at least one metastable anionic state, we have consequently analysed the possibility that condensation reactions, leading to PAHs formation in PPN atmospheres, could occur with negative aromatic species such as stabilized anionic ortho-benzyne (o-C6H4-).To account for this task, through accurate quantum dynamical modelling of the initial steps, we find that, once the primary electron attachment on the neutral ortho-benzyne has taken place producing the corresponding metastable negative ion, the evolution of this resonant anionic intermediate in terms of its energy locations and lifetimes suggests the possibility of a radiationless stabilization by a very rapid intramolecular vibrational redistribution (IVR) of the excess energy carried by the attached electron.Currently,always in the low-energy range (0-5 eV), we are studying the formation mechanisms and evolution of metastable anions of both coronene, given its role in the UV extinction processes due to its charge state, and linear polyynes having permanent dipole.
Carelli F.
Gianturco Francesco A.
Sebastianelli F.
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