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Title: A Small Fullerene (C{sub 24}) may be the Carrier of the 11.2 μ m Unidentified Infrared Band

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 intensitiesmore » 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.« less

Authors:
;  [1];  [2];  [3]
  1. Spectral Sciences, Inc., 4 Fourth Ave., Burlington, MA 01803 (United States)
  2. Thule Scientific, P.O. Box 953, Topanga, CA 90290 (United States)
  3. Wopeco Research, 125 South Great Road, Lincoln, MA 01773 (United States)
Publication Date:
OSTI Identifier:
22663738
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 836; 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; APPROXIMATIONS; DENSITY; DENSITY FUNCTIONAL METHOD; EMISSION; ENERGY SPECTRA; FULLERENES; HYDROGEN; LIFETIME; MOLECULES; PHOTONS; ROTATION; SIMULATION; SPHERICAL CONFIGURATION; SYMMETRY

Citation Formats

Bernstein, L. S., Shroll, R. M., Lynch, D. K., and Clark, F. O., E-mail: larry@spectral.com, E-mail: rshroll@spectral.com, E-mail: dave@caltech.edu, E-mail: frank.clark@gmail.com. A Small Fullerene (C{sub 24}) may be the Carrier of the 11.2 μ m Unidentified Infrared Band. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA5C89.
Bernstein, L. S., Shroll, R. M., Lynch, D. K., & Clark, F. O., E-mail: larry@spectral.com, E-mail: rshroll@spectral.com, E-mail: dave@caltech.edu, E-mail: frank.clark@gmail.com. A Small Fullerene (C{sub 24}) may be the Carrier of the 11.2 μ m Unidentified Infrared Band. United States. doi:10.3847/1538-4357/AA5C89.
Bernstein, L. S., Shroll, R. M., Lynch, D. K., and Clark, F. O., E-mail: larry@spectral.com, E-mail: rshroll@spectral.com, E-mail: dave@caltech.edu, E-mail: frank.clark@gmail.com. Mon . "A Small Fullerene (C{sub 24}) may be the Carrier of the 11.2 μ m Unidentified Infrared Band". United States. doi:10.3847/1538-4357/AA5C89.
@article{osti_22663738,
title = {A Small Fullerene (C{sub 24}) may be the Carrier of the 11.2 μ m Unidentified Infrared Band},
author = {Bernstein, L. S. and Shroll, R. M. and Lynch, D. K. and Clark, F. O., E-mail: larry@spectral.com, E-mail: rshroll@spectral.com, E-mail: dave@caltech.edu, E-mail: frank.clark@gmail.com},
abstractNote = {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.},
doi = {10.3847/1538-4357/AA5C89},
journal = {Astrophysical Journal},
number = 2,
volume = 836,
place = {United States},
year = {Mon Feb 20 00:00:00 EST 2017},
month = {Mon Feb 20 00:00:00 EST 2017}
}