Ni(O2) complex by anion photoelectron spectroscopy

We report the first anion photoelectron spectroscopic study of nickel monoxide ~NiO!, nickel dioxide ~ONiO!, and nickel-O2 complex, Ni~O2!. The adiabatic electron affinity ~EA! of NiO is measured to be 1.46 ~2! eV. Five low-lying electronic excited states (A P , a D , B F , b S, c P) are observed for NiO at 0.43 ~4!, 0.94 ~4!, 1.24 ~3!, 1.80 ~10!, and 2.38 ~10! eV above the ground state, respectively. Two isomers are observed for NiO2, i.e., the linear ONiO dioxide and the Ni~O2! complex. The dioxide has a high EA of 3.05 ~1! eV while the Ni~O2! complex has a rather low EA of 0.82 ~3! eV. Two low-lying excited states are observed for ONiO at 0.40 ~2! and 0.77 ~3! eV above the ground state, respectively. The vibrational frequency of the n1 mode of the ground state ONiO (X Sg ) is measured to be 750 (30) cm. The excited states of the Ni~O2! complex give broad photodetachment features starting at about 1.1 eV above the ground state. Information about the electronic structures of the nickel oxide species and chemical bonding between Ni and O and O2 is obtained and discussed. © 1997 American Institute of Physics. @S0021-9606~97!00525-4#