Chemical bonding between Cu and oxygen-copper oxides vs O-2 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 P-2 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 CuO- plus O-2. 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 O-2. For CuO4-, two isomers are observed. One of them undergoes photodissociation at 3.49 eV, and it is shown to be a Cu/O-2 complex, Cu(O-2)(2)(-). The second isomer yields spectra identical to that of the linear OCuO- with a slight energy shift and is concluded to be an OCuO- solvated by a very weakly bonded O-2, (OCuO-)O-2. CuO6- is shown to exhibit similar behaviors as CuO4- with a Cu/O-2 complex, Cu(O-2)(3)(-), and an O-2-solvated CuO2-, (OCuO-)(O-2)(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 O-2, (OCuO2-)O-2.