Gas phase multicollisional reactions of metal cluster cations with water molecules

Abstract

Reactions within complexes consisting of metal cluster cations and water molecules have been studied using a pulsed arc cluster source (PACS) and a reflectron time-of-flight mass spectrometer. The mass spectra obtained from metal–water cluster ions reveals extensive dehydrogenation of the associated water molecules resulting in the formation of metal-oxide clusters of the general form M_MO_P(OH)⁺ (where M=copper, barium and holmium). For clusters with barium, and holmium, the dehydrogenation occurs from P1 and for copper for P3. These metal oxide and hydroxide products are more abundant than both that of the bare metal clusters M_M⁺ and the associated hydrated metal clusters M_M⁺(H₂O)_N. The stability of the metal oxide clusters as determined by the relative abundances of these species as a function of N and P is seen to correspond to oxidation numbers accessible to the metal ions. The correspondence between the formal oxidation number of a metal and its propensity for oxide formation is investigated. Possible mechanisms for the formation of the observed complex ions are proposed. For complexes containing Ho_M⁺ the variation of the abundances with cluster size is discussed.