Stability and reactivity patterns of medium-sized vanadium oxide cluster cations V_xO_y⁺(4x14)

Gas-phase vanadium oxide clusters V_xO_y⁺ in the size range 4x14 have been produced via laser vaporisation in a continuous flow of He/O₂ carrier gas. The cluster distributions were subsequently characterised by their scattering behaviour at low-density gas targets (10⁻⁴−2×10⁻³ mbar). The experimental scattering cross sections were used to study differences in the interactions with rare gases, hydrocarbons (alkanes: methane, propane, n-butane and alkenes: ethene, propene, but-1-ene) and also small inorganic molecules (N₂, O₂, CO, NO, SO₂). The compositions of the dominant oxide clusters reveal the predominance of vanadium atoms in the formal oxidation states +4 and +5. The interaction patterns of these oxide clusters with rare gases show no indications for fragmentation at collision energies corresponding to a cluster beam velocity of 900 ms⁻¹. Clusters with a composition of (V₂O₅)_n⁺ have increased cross sections for the interaction with alkanes and alkenes. Indeed, for the alkenes stable adducts have been detected under the applied scattering conditions. The increased cross sections have been interpreted in terms of a strong reactivity towards hydrocarbons, which is in agreement with previous results on smaller vanadium oxide clusters (R. C. Bell, K. A. Zemski, K. P. Kerns, H. T. Deng and A. W. Castleman, Jr., J. Phys. Chem. A, 1998, 102, 1733).