Rõõm T, Peedu L, Ge M, Hüvonen D, Nagel U, Ye S, Xu M, Bačić Z, Mamone S, Levitt MH, Carravetta M, Chen JYC, Lei X, Turro NJ, Murata Y, Komatsu K. Infrared spectroscopy of small-molecule endofullerenes.
Philos Trans A Math Phys Eng Sci 2013;
371:20110631. [PMID:
23918713 DOI:
10.1098/rsta.2011.0631]
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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.
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