Laser Ablation Mass Spectrometry of Pyrolyzed Koppers Coal-Tar Pitch:  A Precursor for Fullerenes and Metallofullerenes

• Published in: The journal of physical chemistry. B 1999-11, Vol.103 (44), p.9450-9458
• Main Authors: Zhang, Rui, Achiba, Yohji, Fisher, Keith J, Gadd, Gerard E, Hopwood, Femia G, Ishigaki, Toshinobu, Smith, Derek R, Suzuki, Shinzo, Willett, Gary D
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp9910791

Pyrolyzed Koppers coal-tar pitch samples consisting mainly of polycyclic aromatic hydrocarbons were studied by direct laser vaporization Fourier transform ion cyclotron resonance and time-of-flight mass spectrometry. Fullerene cations were readily formed from these carbonaceous precursors over a wide range of low-laser ablation power densities. The laser-desorption ionization of the pyrolyzed coal-tar pitches shows the presence of a range of polyaromatic hydrocarbons some containing as many as 70 carbon atoms, which should require only small amounts of laser energy to convert them into fullerenes. Metallofullerene formation also occurs with low power laser ablation of pyrolyzed mixtures of metal oxides, metal sulfides, or metal carbonates and the Koppers coal-tar pitch. Ablation with two different laser pulse widths of 230 μs and 8 ns, at a laser wavelength of 1064 nm, shows that only the long-pulse low-power (200−2000 kW cm-2) laser radiation produces metallofullerene ions. The short-pulse high-power (1−2300 MW cm-2) laser ablation results only in the formation of small metal carbide cluster and fullerene ions. Collision-induced dissociation experiments were used to study the structures of the small metal carbide clusters and the endohedral metallofullerene ion, La@C60 +.