Cross sections for collision-induced dissociation (CID) of Fe+n with Xe, 2≤n≤10, are presented. Experiments were performed on a newly constructed guided ion beam mass spectrometer, the design and capabilities of which are described in detail. The single mechanism for dissociation of iron cluster ions is sequential loss of iron atoms with increasing collision energies. There is no evidence for fission to molecular neutral products. The cross section threshold energy dependences are analyzed to give the bond dissociation energies (BDEs), D0(Fe+n−1–Fe). Data analysis employs an empirical model that incorporates RRKM theory to account for inefficient dissociation on the time scale of the experiment. Results show that Fe+6 has the strongest BDE, D0(Fe+5–Fe) =3.44±0.18 eV, while Fe+3 is the most weakly bound, D0(Fe+2–Fe) =1.64±0.15 eV. Neutral cluster BDEs are derived from ionic binding energies and known ionization potentials. Branching ratios and other cross section features are also discussed with respect to cluster size.
In this paper, we present collision-induced-dissociation (CID) studies of gas-phase Fe2+. Experiments were performed on a new guided ion beam mass spectrometer designed to produce cold, mass-selected ions. The energy dependence of the cross section for CID with Xe is presented. Interpretation of the cross-section threshold is consistent with theoretical models and gives D°(Fe2+) = 2.72 ± 0.07 eV. Combined with the known ionization potentials and electron affinities of Fe and Fe2, this bond energy also provides D°(Fe2) = 1.15 ± 0.09 eV and Z)°(Fe2-) = 1.90 ± 0.09 eV. These dimers are discussed with regard to previous work and their respective bonding schemes.
The kinetic energy dependence of collision-induced dissociation (CID) of Co; (n=2-18) with xenon is studied by using a guided ion beam mass spectrometer. Examination of the general dissociation behavior over a broad collision energy range shows that cobalt cluster cations dissociate exclusively by loss of single atoms (cluster "evaporation"), with no evidence found for elimination of molecular cluster fragments. Bond dissociation energies for cobalt cluster cations, Co; (n=2-18), are determined from measurements of the CID thresholds. Bond energies for neutral cobalt clusters, COn (n=4-18), are derived by combining these cationic bond energies with ionization energies for COn from the literature. The dependence of binding energy on cluster size is similar to that observed for iron clusters, and inspires some speculation regarding cluster ion structures.
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