Collision-induced dissociation of Co+n (n=2–18) with Xe: Bond energies of cationic and neutral cobalt clusters, dissociation pathways, and structures

Abstract

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.

Structure, bonding, and magnetism of cobalt clusters from first-principles calculations

“…The Co atoms in dimer have bonding configuration closer to 3d 8 4s 1 than that of the isolated Co atom, which is 3d 7 4s 2 and in addition to the highly delocalized 4s electrons, the more localized 3d electrons also contribute strongly to the bonding, 24 which consequently, produces a shorter bond length for the dimer. Compared to the neutral Co 2 dimer, the experimentally 23,25,26 28 We found that Co 2 dimer has a total magnetic moment of 4 µ B , which is also consistent with mass spectroscopic measurement 22 . Our estimates agree with the previous first-principles calculations.…”

“…The first experimental estimation of Co 2 dimer bond length and binding energy has been made by mass spectroscopy, 22 which are 2.31Å and 1.72 eV, respectively. However, more recent collision-induced dissociation (CID) experiment 23 has estimated an upper bound of 1.32 eV to the dimer dissociation energy. The present calculation gives dimer binding energy as 1.45 eV/atom and a bond length of 1.96Å, which is 78% of the bulk hcp Co.…”

“…32 The bonding in Co + 3 cation is stronger than the neutral Co 3 as it is the case for dimer. 23 Yoshida et al 33 reported that Co…”

“…Generally, the single channel dissociation energy is the most favorable except for n =4, where the dimer dissociation (Co 4 → Co 2 + Co 2 ) is more favorable than the single channel (Co 4 → Co 3 + Co) dissociation. Table II shows the theoretically computed single channel bond dissociation energy compared to the experimentally measured values 23 for the entire range of clusters having sizes 2 to 20.…”

Ab initio Study of Geometries and Magnetic Properties of Small Co Clusters

“…According to the results of test calculations summarized in Table I, we adopted the BLYP exchange-correlation functional in the present work. [16] For accurate calculations, we chose an octupole scheme for the multipolar expansion of the charge density and Coulomb potential. In the optimizations, the energy gradient and atomic displacement converge to Hartree.…”