Synthesis and characterization of molybdenum carbide clusters Mo. (formed by laser irradiation of Mo

Laser radiation (XeCl laser, 308-nanometer wavelength) focused into a cell containing Mo[(CO).sub.6] vapor produced ultrafine particles in the extended waist of the laser beam. Negative ion mass spectrometry revealed molybdenum carbide cluster ions with a stoichiometry [Mo.sub.n][C.sub.4n] (n = 1 to 4). The [Mo.sub.n][C.sub.4n] - (n = 2 to 4) ions are completely unreactive with [NH.sub.3], [H.sub.2]O, and [O.sub.2], suggesting structures in which the molybdenum atoms are unavailable for coordination to additional ligands. Collision-induced dissociation studies of these anions show the loss of [MoC.sub.4] units as the main fragmentation pathway. This observation, together with the lack of addition reactions, provides a basis for structures in which a planar cluster of two, three, or four molybdenum atoms is surrounded by, and bonded to, carbon dimers.