A Small Fullerene (C24) may be the Carrier of the 11.2 micron Unidentified Infrared Band
| Autor: | Bernstein, L. S., Shroll, R. M., Lynch, D. K., Clark, F. O. |
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| Rok vydání: | 2017 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| DOI: | 10.3847/1538-4357/aa5c89 |
| Popis: | We analyze the 11.2 {\mu}m unidentified infrared band (UIR) spectrum from NGC 7027 and identify a small fullerene (C24) 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 non-polar molecule and precluding rotational emission. Its rotational temperature should be well approximated by that measured for non-polar molecular hydrogen, ~825 K for NGC 7027. Using this temperature, and the inferred spherical symmetry, we perform a spectral fit to the intrinsic profile that results in a rotational constant implying C24 as the carrier. We show that the spectroscopic parameters derived for NGC 7027 are consistent with the 11.2 {\mu}m UIR bands observed for other objects. We present density functional theory (DFT) calculations for the frequencies and infrared intensities of C24. 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 C24 SED is consistent with the entire UIR spectrum and is the dominant contributor to the 11.2 and 12.7 {\mu}m bands. Comment: 20 pages, 8 figures, accepted for publication in ApJ, replaced incorrect figure 8 |
| Databáze: | arXiv |
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