title: Dissociation of gas-phase bimetallic clusters as a probe of charge densities: the effective charge of uranyl.
abstract: Complementary experimental and computational methods for evaluating relative charge densities of metal cations in gas-phase clusters are presented. Collision-induced dissociation (CID) and/or density functional theory computations were performed on anion clusters of composition MM'A(m+n+1)(-), where the two metal ions have formal charge states M(m+) and M'(n+) and A is an anion, NO3(-), Cl(-), or F(-) in this work. Results for alkaline earth and lanthanide metal ions reveal that cluster CID generally preferentially produces MA(m+1)(-) and neutral M'An if the surface charge density of M is greater than that of M': the metal ion with the higher charge density takes the extra anion. Computed dissociation energies corroborate that dissociation occurs via the lowest energy process. CID of clusters in which one of the two metal ions is uranyl, UO2(2+), shows that the effective charge density of U in uranyl is greater than that of alkaline earths and comparable to that of the late trivalent lanthanides; this is in accord with previous solution results for uranyl, from which an effective charge of 3.2+ was derived.
authors.affiliation: Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa , Estrada Nacional 10, km 139.7, 2695-066 Bobadela LRS, Portugal.
authors.forename: Ana F
authors.initials: AF
authors.lastname: Lucena
authors.forename: José M
authors.initials: JM
authors.lastname: Carretas
authors.forename: Joaquim
authors.initials: J
authors.lastname: Marçalo
authors.forename: Maria del Carmen
authors.initials: Mdel C
authors.lastname: Michelini
authors.forename: Philip X
authors.initials: PX
authors.lastname: Rutkowski
authors.forename: John K
authors.initials: JK
authors.lastname: Gibson