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In our recent investigation of the IR spectrum of CO physically adsorbed on C60 films, two well-resolved absorption bands at 2135 and 2128 cm -1 were found, suggesting that the molecule is adsorbed on two different sites. To determine the nature of these adsorption sites, calculations of adsorption potentials and spectral shifts for the CO/C60 system were performed. The calculations were done for the fcc (100), fcc ( 111) hcp (001), and hcp (111) surface planes. In the calculations the 6-exponential and the Lennard-Jones potentials were used. A number of adsorption sites were chosen. These included the void space between four, three, and two neighboring C60 molecules and the center of the hexagon and the pentagon on the C60 surface. The calculated potentials and spectral shifts clearly indicate that adsorption sites in the voids between the C60 molecules are energetically preferred over sites on top of single C60 molecules. Comparison is made between results obtained with the two potentials and with results obtained previously with the two other carbon allotropes: graphite and diamond.

Infra-red spectra of CO adsorbed on NaCl, NaBr and NaI films were recorded at -196°C and for different surface coverages. The high surface area films were prepared by a method described previous1y.l The absorption bands were shifted, with respect to the gas phase, towards higher energies. For NaCl as adsorbent, the heat of adsorption was calculated for various adsorption sites and orientations of the adsorbate, and was found in agreement with experiment for molecules adsorbed perpendicularly on the surface Naf ions. A high contribution from the quadrupole field-gradient interaction was found. Spectral shifts were calculated, using the perturbation method. The perturbing potential was taken as a sum of four attractive and repulsion potentials. Good agreement with the experimental value of Av was found.

The adsorption of CO and NO on c 6 0 is studied using the technique of IR spectroscopy. The IR spectra of CO show two absorption bands, which indicate the presence of two adsorption sites on the C,, surface. The IR spectra of NO show, in addition, a multiplicity in the two absorption bands, which indicates that NO is adsorbed in its dimer form on two sites. Large spectral shifts are observed on adsorption of both CO and NO on C60, demonstrating that the interaction of these gases with c 6 0 is relatively strong. of carbon. The differences in behavior were related to the structure Of c60. (1) Kroto, H. W.; Allaf, A. W.; Baln, S . P. Chem. Rev. 1991, 91, (2) Tsidoni, E.; Kozirovski, Y.; Folman, M.; Heidberg, J. J. Electron 1213-1235.Photoexcited triplet and photoinduced doublet states of Cm oriented in a nematic liquid crystal (LC) and toluene, were studied by time-domain EPR. The data indicate that in both matrices, 3Cm undergoes temperature dependent molecular rotation. However, whereas in the LC the rotation rate is increased monotonously between 7 and 298 K, the dynamics in toluene depends strongly on its phase diagram. About the melting point of toluene, a polarized doublet is observed concurrently with the disappearance of the triplet. At higher temperatures, where the liquid phase prevails, the dynamics of the photoinduced doublet suggests an unpaired electron delocalized on an aggregate of CM in toluene, with relatively long-lived magnetization of -25 MS.

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