Mass spectroscopy and reaction studies of laser-vaporized clusters from metal-doped carbon materials

Metal-carbon binary clusters are believed to be important precursor clusters both for single-walled carbon nanotubes (SWNTs) and endohedral metallofullerene. Metal-carbon binary clusters (MC_n M = La, Ni or Co) and carbon clusters (C_n) were generated with a pulsed laser-vaporization supersonic-expansion cluster beam source directly connected to the FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometer, and chemical reaction of MC_n^- and C_n^- with nitric oxide was studied. Depending on the metal element, the generation efficiency and the reactivity of metal-carbon binary clusters were completely different. LaC_n^- (n=even, n≥36) was much less reactive to NO than pure carbon clusters, while MC_n^- (M = Ni or Co) was much more reactive than pure carbon clusters. It was speculated that LaC_n^- (n=even, n≥36) had a fullerene-like cage structure with a metal atom inside, and that MC_n^- (M = Ni or Co) had an imperfect cage structure where a metal atom preferentially attached to the imperfect site.