A Small Fullerene (C24) may be the Carrier of the 11.2 micron
  Unidentified Infrared Band
  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.
