ISOTOPE FRACTIONATION IN THE SYNTHESIS OF FULLERENES

The synthesis of fullerenes by the direct current (DC) carbon arc evap oration method produces a number of different carbon materials. This i nvestigation has involved the structural characterisation of the mater ials and the study of their isotopic composition. The cathode deposit was a highly ordered graphite with the basal planes oriented in the ax ial direction of the graphite rod. Raman microprobe spectroscopy, X-ra y powder diffraction, and temperature programmed combustion measuremen ts also showed that the material was heterogeneous. The structural cha racterisation results were consistent with the deposit being formed at progressively lower heat-treatment temperatures with increasing depos ition. The fullerene soot was a very heterogeneous material with a lar ge surface area. Isotope composition studies showed that the raw fulle rene soot, fullerene depleted soot (toluene extract), C60, and C70 wer e enriched in C-13 relative to the graphite anode, whereas the cathode deposit was depleted in C-13. The measurements show that C60 is riche r in C-13 compared with both C70 and the toluene-extracted soot. The i mplications regarding the mechanisms for the formation of fullerenes a re discussed.