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 3 x 3 x 3 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 are 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 TimCm- clusters including Ti13C22 are located at masses slightly above the fee cubic shell closings. The shift can be explained by the bonding of additional C atoms at the corners of tho cubes.