Collision-induced dissociation studies of FemOn+ : Bond energies in small iron oxide cluster cations, FemOn+ (m=1–3, n=1–6)

Abstract

A variety of iron oxide cluster cations is synthesized in a laser vaporization ion source. The kinetic energy dependence of the collision-induced dissociation (CID) of mass selected Fe(m)O(n) (+) (m=1-3, n=1-6) clusters with Xe is studied in this work using a guided ion beam tandem mass spectrometer. Examination of the general dissociation behavior over a broad collision energy range (0-15 eV) shows that iron oxide clusters can dissociate via evaporation of neutral Fe and O atoms as well as fission by loss of neutral O(2), FeO, FeO(2), Fe(2)O(2), and Fe(2)O(3) fragments. Such fission pathways, which are not observed in the CID studies of pure Fe cluster cations and most other pure transition metal cluster cations, result from the strong iron oxygen bonds. In general, the predominant dissociation pathways are found to correlate with the oxidation state of the iron in the cluster. Thresholds for loss of neutral Fe, O, O(2), FeO, FeO(2), Fe(2)O(2), and Fe(2)O(3) from various iron oxide cluster cations are quantitatively determined. These values are used to determine bond energies and heats of formation for both neutral and cationic iron oxide clusters in this size range.