Formation, Structures, and Reactivities of Niobium Oxide Cluster Ions

Niobium oxide cluster ions are produced by a laser-induced plasma source. The cluster distribution, collision-induced dissociation (CID), and cluster reactivities are studied using a triple-quadrupole mass spectrometer. CID experiments on the cluster ions Nb 3 O 7 - 9 +, Nb 4 O 9 - 11 +, and Nb 5 O 12 + reveal that their building blocks are Nb 2 O 5, NbO 2 +, NbO 3, Nb 3 O 7 +, O, and O 2, whereby the cluster stoichiometry is assigned to have the general form (NbO 3 ) m (NbO 2 ) n (O) 0 - 4 + . The trends in the ionization potentials of these species are estimated in terms of the CID fragments produced. Nb 3 O 8 - 9 + and Nb 4 O 11 + cluster ions evidently form via the adsorption of one oxygen atom or molecule onto the cluster surface. Nb 3 O 7 +, Nb 4 O 9 +, and Nb 5 O 12 + have strong reactivities to abstract an oxygen atom from oxygen-containing molecules and adsorb small hydrocarbons at near thermal energies. In particular, the reactivity of the oxygen atom or molecule in the oxide clusters Nb 3 O 8 - 9 + and Nb 4 O 11 + is consistent with our suggestions that it has a radical oxygen character.