Reactivities and collision-induced dissociation of vanadium oxide cluster cations

Reactivities and collision-induced dissociation of vanadium oxide cluster cations are investigated using a triple quadrupole mass spectrometer coupled with a laser vaporization source. The dominant peaks in the mass distribution correspond to cluster ions with stoichiometries of (VO2)(n)(V2O5)(m)(O-2)(q)(+) Collision-induced dissociation studies of the vanadium oxide species V2O4-6+, V3O6-9+, V4O8-10+, V5O11-13+, V6O13-15+, and V7O16-18+ show that VO2, VO3, and V2O5 units are the main building blocks for most of these clusters. The reaction pathways observed for these vanadium oxide clusters include molecular association, cracking, dehydration, and oxygenation of the neutral hydrocarbons with the reactivities of specific clusters differing from species to species. For example, V3O7+ is very efficient in the dehydrogenation of 1,3-butadiene and in the cracking of 1-butene. On the other hand, V3O6+ produces only molecular association products with these same reactants. To help explain these differences in reactivity, calculations on the molecular structure of some of these cluster ions were also undertaken, and the findings are presented.