Chemical Bonding between Cu and OxygensCopper Oxides vs O2 Complexes: A Study of CuOx (x ) 0-6) Species by Anion Photoelectron Spectroscopy

An extensive photoelectron spectroscopic study on the CuOx (x ) 0-6) species is presented. The photoelectron spectra of these species are obtained at four detachment photon energies: 2.33, 3.49, 4.66, and 6.42 eV. The spectra of the copper atom are included to show the dependence of the detachment cross sections on the photon energies. An intense two-electron transition to the 2P excited state of Cu is also observed in the 6.42 eV spectrum of Cu-. For CuO-, we observe an excited state of the anion, as well as photodetachment transitions to charge transfer excited states of CuO (Cu2+O2-). Six transitions are observed for CuO2 at 6.42 eV, revealing all six valence molecular orbitals of the linear OCuO molecule. CuO3 is observed to undergo photodissociation at 3.49 eV to give an internally hot CuOplus O2. It is shown to have an OCuO2 type of structure, and its electronic structure can be viewed to be due to that of CuO perturbed by an O2. For CuO4, two isomers are observed. One of them undergoes photodissociation at 3.49 eV, and it is shown to be a Cu/O2 complex, Cu(O2)2. The second isomer yields spectra identical to that of the linear OCuOwith a slight energy shift and is concluded to be an OCuOsolvated by a very weakly bonded O2, (OCuO)O2. CuO6 is shown to exhibit similar behaviors as CuO4 with a Cu/O2 complex, Cu(O2)3, and an O2-solvated CuO2, (OCuO)(O2)2. The CuO5 spectra are observed to be similar to that of CuO3, and it is shown to be due to a CuO3 solvated by an O2, (OCuO2)O2.