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Philos Trans A Math Phys Eng Sci. 2013 Aug 5;371(1998):20110631. doi: 10.1098/rsta.2011.0631. Print 2013 Sep 13.

Infrared spectroscopy of small-molecule endofullerenes.

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1
National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia. toomas.toom@kbfi.ee

Abstract

Hydrogen is one of the few molecules that has been incarcerated in the molecular cage of C₆₀ to form the endohedral supramolecular complex H₂@C₆₀. In this confinement, hydrogen acquires new properties. Its translation motion, within the C₆₀ cavity, becomes quantized, is correlated with its rotation and breaks inversion symmetry that induces infrared (IR) activity of H₂. We apply IR spectroscopy to study the dynamics of hydrogen isotopologues H₂, D₂ and HD incarcerated in C₆₀. The translation and rotation modes appear as side bands to the hydrogen vibration mode in the mid-IR part of the absorption spectrum. Because of the large mass difference of hydrogen and C₆₀ and the high symmetry of C₆₀ the problem is almost identical to a vibrating rotor moving in a three-dimensional spherical potential. We derive potential, rotation, vibration and dipole moment parameters from the analysis of the IR absorption spectra. Our results were used to derive the parameters of a pairwise additive five-dimensional potential energy surface for H₂@C₆₀. The same parameters were used to predict H₂ energies inside C₇₀. We compare the predicted energies and the low-temperature IR absorption spectra of H₂@C₇₀.

KEYWORDS:

endohedral; fullerene; infrared; para and ortho hydrogen

PMID:
23918713
DOI:
10.1098/rsta.2011.0631
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