An infrared study on CO intercalated in solid C-60

The infrared (IR) absorbance spectra of CO intercalated in solid C-60 have been measured as a function of temperature. The spectra show a gradual tran sition from a nearly free rotation of the CO molecules to a situation where their rotational motion is severely hindered. The hindering of the rotatio nal motion of CO caused by the surrounding C-60 molecules is found to be co mparable to that observed for CO dissolved in a liquid. Good agreement is f ound between quantum mechanically calculated spectra and the measured IR sp ectra. The intermolecular van der Waals vibrations of a CO molecule rattlin g in the octahedral site of the C-60 lattice have been observed at low temp eratures. The IR spectra of CO intercalated in C-70 are measured and compar ed to those observed for CO intercalated in C-60. (C) 1999 American Institu te of Physics. [S0021-9606(99)00904-6].