Anion photoelectron spectroscopy of vanadium-doped cobalt clusters

Bimetallic cobalt (Co)-vanadium (V) clusters, Co_nV_m^- (n = 4-14, m = 0-2), are investigated using anion photoelectron spectroscopy at 4.66 eV photon energy. Electron affinities (EA) and vertical detachment energies (VDE) are determined, and the electronic structures of V- and V₂-doped Co_n clusters are compared to those of pure Co_n clusters. Bonding and hybridization effects can be explained using a charge-transfer model. A peak shape analysis confirms the high stability of the Co₁₂V cluster with a most plausible icosahedral structure with the V atom in the cage center. Together with ionization potentials (IP), the electronic structures of the clusters are compared to H₂ chemisorption rate coefficients reported previously. Thus, this study completes the investigation of electronic properties and reactivity of the bimetallic Co_nV_m clusters as a function of charge, size, and distribution. Although the reactivity of Co_nV_m reveals a better correlation toward the EA rather than toward IP, no improved correlation is found between promotion energies and reactivity. This result clearly shows that the chemisorption reactivity of the heterogeneous clusters is largely governed by geometric factors.