THE ROLE OF POLYCYCLIC AROMATIC HYDROCARBONS IN THE STUDY OF FULLERENE FORMATION

Abstract

Two approaches intended to elucidate the fullerene-formation mechanism are presented. The first of these involves pyrolytic synthesis of fullerenes from hydrocarbon ring structures known as polycyclic aromatic hydrocarbons (PAH's). Following work by Taylor et al. (Nature 366, 728, 1993), C60 is be made by heating a naphthalene vapor/argon mixture to approximately 1000°C. The use of several precursor P AH' s, including naphthalene, is examined in this work. The second approach involves the intentional poisoning of carbon-arc fullerene production by the addition of hydrogen (H₂) to the quenching atmosphere. By adding hydrogen in varying amounts one produces both PAH's and chain molecules, possibly representing interrupted steps of the pathway leading to fullerenes. Various analytical techniques are employed to examine both approaches. It is shown by mass spectrometry' that pyrolytic synthesis is not indicative of the fullerene-formation mechanism of the carbon-arc technique pioneered by Krlitschmer et al. (Nature 347, 354, 1990). In addition to mass spectrometry, Fourier-transform infrared and ultra-violet/visible absorption spectroscopy, high-performance Iiquidchromatography, and Raman-scattering spectroscopy are brought to bear in the analysis of the hydrogen-poisoning approach. From the analysis the PAH molecules formed in the hydrogen poisoning of the carbon-arc do not appear to comprise a pathway to fullerene formation. However, there is evidence indicating that chains, produced as a result of hydrogen contamination of the carbon-arc technique, are related to the formation of fullerene molecules.