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Title: Anthracene clusters and the interstellar infrared emission features

The unidentified infrared bands are ubiquitous in the interstellar medium and typically attributed to emission from neutral and ionized polycyclic aromatic hydrocarbons (or PAHs). The contribution of neutral PAH clusters to these bands has been impossible to determine due to a paucity of infrared spectral data. Here we investigated neutral clusters of the three-ring PAH anthracene using FTIR absorption spectroscopy of anthracene matrix-isolated at varying concentrations in solid argon. In order to determine likely cluster structures of the embedded molecules, we also calculated theoretical absorption spectra for the anthracene monomer through hexamer using density functional theory with a dispersion correction (DFT-D). The DFT-D calculations have been calibrated for the anthracene dimer using the second-order Møller-Plesset approach. Because there is some support for the hypothesis that three or four-ring PAHs are present in the Red Rectangle nebula, we discuss the application of our results to this nebula in particular as well as to the interstellar infrared emission in general.
Authors:
 [1] ;  [2] ;  [3]
  1. NASA Ames Research Center, Mail Stop 245-6, Building N245, Room 148, P.O. Box 1, Moffett Field, CA 94035 (United States)
  2. SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, CA 94043 (United States)
  3. NASA Ames Research Center, Moffett Field, CA 94035 (United States)
Publication Date:
OSTI Identifier:
22351603
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 783; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; CORRECTIONS; COSMOLOGY; DENSITY FUNCTIONAL METHOD; DISPERSIONS; EMISSION; FOURIER TRANSFORM SPECTROMETERS; INFRARED SPECTRA; INTERSTELLAR SPACE; MOLECULES; NEBULAE; POLYCYCLIC AROMATIC HYDROCARBONS