The photoelectron spectra of small gas-phase YnOm- clusters (n = 2-10, m = 1-3) are measured at photon energies of 3.49 and 4.66 eV. Cluster generation is performed with the aid of laser vaporization, whereas the kinetic energy of electrons is measured using a magnetic bottle photoelectron spectrometer. The evolution of the electronic structure of neutral yttrium oxide clusters is discussed in terms of both sequential oxygen addition to the metal cluster core and sequential metal atom increase. Electron affinities and vertical detachment energies are measured and compared to ionization potentials of the monoxide cluster series [Knickelbein, M. J. Chem. Phys. 1995, 102, 1]. A general trend in the observed photoelectron spectra is a shifting of threshold energies to higher binding energies with increasing cluster size n. At low electron binding energies, main spectral features are contributed from metal d-band orbitals whereas the O 2p contribution becomes apparent with increasing oxygen content due to a higher degree of hybridization of yttrium s, d, and oxygen 2p orbitals. The differences of yttrium-oxygen dissociation energies are determined and compared.
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