Author/Authors :
F. and Joblin، نويسنده , , C. and Tielens، نويسنده , , A.G.G.M. and Allamandola، نويسنده , , L.J. and Léger، نويسنده , , A. and dʹHendecourt، نويسنده , , L. and Geballe، نويسنده , , T.R. and Boissel، نويسنده , , P.، نويسنده ,
Abstract :
Using recent laboratory measurements on gas-phase polycyclic aromatic hydrocarbons (PAHs) as well as new astronomical observations, we discuss the origin of the 3.3 μm emission band and of its major satellite band at 3.40 μm. These studies show that the position, width and profile of the 3.3 μm band are consistent with the carriers being free PAH molecules. The peak position and width of this band are sensitive to the emission temperature (i.e. absorbed UV photon). The observed peak position and width correspond to an “average” emission temperature of 1200 K which implies a size of 24 and 48 carbon atoms for a 6 and 10 eV absorbed photon, respectively. The first overtone of the 3.3 μm hand has been detected at 1.68 μm in the planetary nebula IRAS 21282+5050. These observations imply that the hot band is expected at 3.43 μm rather than at 3.40 μm. The main 3.40 μm band is attributed to the CH stretching mode from methyl side groups attached to the periphery o f PAHs. This assignment is supported by the spectral agreement with laboratory spectra and by the behavior of the 3.40 μm band upon UV radiation field in astronomical environments.
