Chemical Reaction of Metal-carbon Binary Cluster Anions by Ft-icr Mass Spectrometer

Metal-carbon binary clusters generated by the laser vaporization of metal-doped carbon materials used for macroscopic production of endohedral metallofullerene or SWNTs were studied. Positive and negative clusters generated by the laser-vaporization supersonicexpansion cluster beam source were directly injected to the FT-ICR mass spectrometer. Depending on the metal species, the generated cluster distributions were drastically different. The chemical reaction of these clusters with NO was used as the probe of the structure of clusters. LaC2n, ScC2n and YC2n from La-doped, Sc-doped and Ni/Y-doped carbon samples, respectively, were much less reactive to NO compared with pure carbon clusters. On the other hand, NiCn from Ni/Co-doped and Ni/Ydoped materials was much more reactive than pure carbon clusters. Through comparisons with the molecular dynamics simulations, it was speculated that La, Sc and Y were inside the annealed “random-cage” carbon structure even at small size as M@C44. Through experiments of Ni/Co and Ni/Y doped samples for SWNT generation, carbon clusters with Y atom inside the random cage and only a small amount of carbon clusters with a Ni atom were observed. However, a drastic enhancement of even-odd alternations in pure carbon distribution was observed. The efficient generation of “random cage” structures starting from C36 might be the important step in the generation mechanism of SWNT.