Detalles de publicación
PP 06009
"Hydrogenated fullerenes and the anomalous microwave emission of the dark cloud LDN 1622"
Instituto de Astrofísica de Canarias
We study the rotation rates and electric dipole emission of hydrogenated
icosahedral fullerenes under the physical conditions of the
dark cloud LDN 1622. The abundance of fullerenes is estimated by fitting
theoretical photoabsorption spectra to the characteristics of
the UV bump extinction in dark clouds. The UV bump appears to be well reproduced by a mixture of fullerenes following a size distribution power law, which gives progressively lower abundances as the radius of the fullerene increases. We infer abundances
of order 0.2x10^{-6}n(H_2) for C_{60}. A significant fraction of these molecules are expected to be hydrogenated. We compute the electric dipole rotational emission from these fullerene hydrides taking into account rotational excitation and damping processes. The recent detection of anomalous microwave emission (5-60 GHz) in LDN 1622 by Casassus et al. can be explained as the result of electric dipole radiation from hydrogenated fullerenes. The bulk of the emission (10-30 GHz) appears to be associated
with 60-80 carbon atoms fulleranes with a degree of hydrogenation of C:H $\approx$ 3:1. A small contribution ($\sim$10\%) of these molecules residing in the surrounding cold neutral medium and/or photodissociation region of the cloud is required to fit the high frequency tail (40-60 GHz) of the emission.
icosahedral fullerenes under the physical conditions of the
dark cloud LDN 1622. The abundance of fullerenes is estimated by fitting
theoretical photoabsorption spectra to the characteristics of
the UV bump extinction in dark clouds. The UV bump appears to be well reproduced by a mixture of fullerenes following a size distribution power law, which gives progressively lower abundances as the radius of the fullerene increases. We infer abundances
of order 0.2x10^{-6}n(H_2) for C_{60}. A significant fraction of these molecules are expected to be hydrogenated. We compute the electric dipole rotational emission from these fullerene hydrides taking into account rotational excitation and damping processes. The recent detection of anomalous microwave emission (5-60 GHz) in LDN 1622 by Casassus et al. can be explained as the result of electric dipole radiation from hydrogenated fullerenes. The bulk of the emission (10-30 GHz) appears to be associated
with 60-80 carbon atoms fulleranes with a degree of hydrogenation of C:H $\approx$ 3:1. A small contribution ($\sim$10\%) of these molecules residing in the surrounding cold neutral medium and/or photodissociation region of the cloud is required to fit the high frequency tail (40-60 GHz) of the emission.