INDUCED INFRARED ABSORPTION OF $H_{2}$ IN SOLID $C_{60}$
Loading...
Date
2002
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
We use infrared spectroscopy to observe the quantum dynamics of molecular hydrogen trapped within the interstitial sites of the $C_{60}$ lattice. These spectra form the first observation of infrared activity induced by the $C_{60}$ intermolecular potential. They also reveal the first evidence for distinct side-bands (at +/- $127 cm^{-1}$) associated with the translational motion of the trapped species. On exposure of $C_{60}$ to high pressure $H_{2}$ the induced modes grow in intensity over the course of a few hours as the $H_{2}$ slowly diffuses into the octahedral interstitial sites. Despite the fact that the fundamental $H_{2}$ vibrational mode occurs highly red-shifted ($54 cm^{-1}$) relative to the gas phase the location of the rotatioanal side-bands indicates almost complete rotational freedom of the trapped $H_{2}$. Most surprisingly the spectra contain weak central zero-phonon modes which should not be activated by a potential with true octahedral symmetry. These zero-phonon modes show a sudden decrease in intensity on cooling through the $C_{60}$ orientational phase transition at 260 K. We speculate that this may be the result of freezing out of a quasi fluid like surface layer within the $C_{60}$ lattice. Work supported by Research Corporation Grant \# CC5240
Description
Author Institution: DEPARTMENT OF PHYSICS, OBERLIN COLLEGE