Production of large metallocarbohedrene clusters using a pulsed arc cluster ion source

The hypothesis of the existence of multi-cage structures of metallocarbohedrene clusters ("metcars" ) bases on the observation of certain magic numbers in the mass spectra corresponding to an excess of carbon atoms with respect to the bulk stochiometry (1:1 for TiC). E.g., the appearance of the magic number cluster Ti13C22 has been explained by assuming a double-cage structure. However, the same magic number can be assigned to a 3x3x3 cube (= Ti13C14) with 8 additional carbon atoms forming carbon dimers at the corners of the cube. We recorded mass spectra of TinCm clusters using a pulsed arc cluster ion source with an additional annealing discharge. For the positive ions, Ti8C12+ is the major peak in the mass spectrum. For the anions, much larger clusters could be generated. The maxima of the larger TinCm- clusters including Ti13C22- are located at masses slightly above the fcc cubic shell closings. The shift can be explained by the bonding of additional C atoms at the corners of the cubes