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Author Bernstein, L. S. ♦ Shroll, R. M. ♦ Lynch, D. K. ♦ Clark, F. O.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ ABSORPTION ♦ APPROXIMATIONS ♦ DENSITY ♦ DENSITY FUNCTIONAL METHOD ♦ EMISSION ♦ ENERGY SPECTRA ♦ FULLERENES ♦ HYDROGEN ♦ LIFETIME ♦ MOLECULES ♦ PHOTONS ♦ ROTATION ♦ SIMULATION ♦ SPHERICAL CONFIGURATION ♦ SYMMETRY
Abstract We analyze the spectrum of the 11.2 μ m unidentified infrared band (UIR) from NGC 7027 and identify a small fullerene (C{sub 24}) as a plausible carrier. The blurring effects of lifetime and vibrational anharmonicity broadening obscure the narrower, intrinsic spectral profiles of the UIR band carriers. We use a spectral deconvolution algorithm to remove the blurring, in order to retrieve the intrinsic profile of the UIR band. The shape of the intrinsic profile—a sharp blue peak and an extended red tail—suggests that the UIR band originates from a molecular vibration–rotation band with a blue band head. The fractional area of the band-head feature indicates a spheroidal molecule, implying a nonpolar molecule and precluding rotational emission. Its rotational temperature should be well approximated by that measured for nonpolar molecular hydrogen, ∼825 K for NGC 7027. Using this temperature, and the inferred spherical symmetry, we perform a spectral fit to the intrinsic profile, which results in a rotational constant implying C{sub 24} as the carrier. We show that the spectroscopic parameters derived for NGC 7027 are consistent with the 11.2 μ m UIR bands observed for other objects. We present density functional theory (DFT) calculations for the frequencies and infrared intensities of C{sub 24}. The DFT results are used to predict a spectral energy distribution (SED) originating from absorption of a 5 eV photon, and characterized by an effective vibrational temperature of 930 K. The C{sub 24} SED is consistent with the entire UIR spectrum and is the dominant contributor to the 11.2 and 12.7 μ m bands.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2017-02-20
Publisher Place United States
Journal Astrophysical Journal
Volume Number 836
Issue Number 2


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