15min:

IWAN HOLEMAN, GERT VON HELDEN, BEAT H. MEIER, AD VAN DER AVOIRD AND GERARD MEIJER, Dept. of Molecular and Laserphysics, University of Nij\-megen, Toernooiveld 1, NL-6525ED Nij\-megen, The Netherlands.

Solid C₆₀ is a promising matrix for the storage of guest species, both inside and in between the cages. It consists only of one type of atoms, and the high molecular symmetry results in well-defined and uniform intercalation sites. In solid C₆₀ (fcc lattice) there are, beside the void inside the C₆₀ molecule, two types of interstitial sites that are available for intercalants, one octahedral site (d=4.1~ Å) and two tetrahedral sites (d=2.2~ Å) per C₆₀ molecule. A reasonable estimate of the `van der Waals length' of a CO molecule is 4.4~ Å, suggesting that the CO molecule snugly fits into the octahedral sites of the C₆₀ lattice.
Via high temperature, high pressure synthesis, samples in which large quantities of CO are trapped in these octahedral sites can be made. Under ambient conditions, the CO remains in the sample for many weeks.
The ro-vibrational motion of the CO molecules in the C₆₀ matrix is studied as a function of temperature by infrared and nuclear magnetic resonance spectroscopy. The observed spectra indicate a gradual transition from nearly free motion of CO at room temperature to hindered motion at low temperature, with only tunneling between symmetry equivalent orientations remaining. The observations are augmented by theory, and details on the local environment of the CO molecules are extracted.