title: Infrared spectroscopy of small-molecule endofullerenes.
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.
authors.affiliation: National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia. toomas.toom@kbfi.ee
authors.forename: T
authors.initials: T
authors.lastname: Rõõm
authors.forename: L
authors.initials: L
authors.lastname: Peedu
authors.forename: Min
authors.initials: M
authors.lastname: Ge
authors.forename: D
authors.initials: D
authors.lastname: Hüvonen
authors.forename: U
authors.initials: U
authors.lastname: Nagel
authors.forename: Shufeng
authors.initials: S
authors.lastname: Ye
authors.forename: Minzhong
authors.initials: M
authors.lastname: Xu
authors.forename: Z
authors.initials: Z
authors.lastname: Bačić
authors.forename: S
authors.initials: S
authors.lastname: Mamone
authors.forename: M H
authors.initials: MH
authors.lastname: Levitt
authors.forename: M
authors.initials: M
authors.lastname: Carravetta
authors.forename: J Y-C
authors.initials: JY
authors.lastname: Chen
authors.forename: Xuegong
authors.initials: X
authors.lastname: Lei
authors.forename: N J
authors.initials: NJ
authors.lastname: Turro
authors.forename: Y
authors.initials: Y
authors.lastname: Murata
authors.forename: K
authors.initials: K
authors.lastname: Komatsu
keywords: endohedral; fullerene; infrared; para and ortho hydrogen