Photoelectron spectroscopy of cobalt oxide cluster anions

Photoelectron spectroscopy of size-selected Co_nO_m^- clusters (n = 4-20; m = 0-2) is performed in a pulsed molecular beam experimental at photon energies of 3.49 and 4.66 eV. Cobalt oxide cluster anions are generated in a laser vaporization source and the photoelectron spectra are measured with a magnetic bottle photoelectron spectrometer. The size-dependent evolution of the electronic structure of the oxide clusters is discussed in terms of cluster composition. Threshold binding energy features are mainly contributed from Co d-derived orbitals throughout the complete series, indicating that the incoming oxygen atoms cause a minor influence on the electronic structures. Although for n > 13 EAs and VDEs of Co_n and Co_nO_m clusters overlap within the experimental resolution, at smaller cluster sizes, the values increase in the order of Co_n < Co_nO < Co_nO₂. For Co₄O₃^- and Co₅O₃^-, the spectra indicate the presence of isomers with low EAs peroxo and ozonide isomers. To compare the different channels of oxygen chemisorption, relative dissociation energies are determined via thermochemical cycles.