Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands - Auto exhaust along the Milky Way
L. J. Allamandola, A. G. G. M. Tielens, J. R. Barker;
ApJ, 1985, 290, L25
ABSTRACT:The unidentified infrared emission features (UIR bands) are attributed to a collection of partially hydrogenated, positively charged
polycyclic aromatic hydrocarbons (PAHs).
This assignment is based on a
spectroscopic analysis of the UIR bands.
Comparison of the observed interstellar
6.2 and 7.7-micron bands with the laboratory measured Raman spectrum of a
collection of carbon-based particulates (auto exhaust) shows a very good
agreement, supporting this identification.
The infrared emission is due to
relaxation from highly vibrationally and electronically excited states.
The
excitation is probably caused by UV photon absorption.
The infrared
fluorescence of one particular, highly vibrationally excited PAH (chrysene) is
modeled.
In this analysis the species is treated as a molecule rather than bulk
material and the non-thermodynamic equilibrium nature of the emission is fully
taken into account.
From a comparison of the observed ratio of the 3.3 to
11.3-micron UIR bands with the model calculations, the average number of carbon
atoms per molecule is estimated to be about 20.
The abundance of
interstellar PAHs is calculated to be about 2 x 10 to the -7th with respect to
hydrogen.
KEYWORDS: aromatic compounds, hydrocarbons, infrared spectra, interstellar matter, milky way galaxy, exhaust emission, fluorescence, molecular excitation, particulates, raman spectra, spectral bands, spectral line width, vibrational spectra
PERSOKEY:dust, pah, mir, ,
CODE: allamandola85