ISOTOPE EFFECTS IN THE RAMAN-SPECTRA OF C-13 ENRICHED C-60

Recent studies carried out on an organic superconductor, beta -(BEDT-T TF)2I3, have shown the important role played by the 13C isotope on the T(c) transition, when substitution is made on the central C-C bond of the molecule. Simultaneously, Raman studies determined the frequency shifts observed in the C=C stretching vibrations in the substituted sa mples and consequently, put in evidence the role of the intramolecular Ag vibrations. We have extended these studies to compounds of the new carbon family, the fullerenes. in which 82% of the carbon atoms were substituted with C-13 in C60. The superconducting transition measured on the same sample doped with potassium is lowered by 1.5 to 2K as com pared to the standard material doped in similar conditions. In the Ram an spectrum, the main Ag band measured at 1467 cm-1 in C-12(60) is shi fted to 1420 cm-1 in enriched C-13(60). Taking into account the ratio between the molecular weigth of the enriched C-13(60) and of the stand ard material, one predicts a theoretical value for this mode at 1418 c m-1 in die enriched sample. A preliminary analysis of the Raman spectr um will be presented.