Negative-ion photoelectron spectroscopy of Cu clusters reacted with NO molecules

Negative ions of copper clusters reacted with nitric oxide molecules are studied by mass-selected photoelectron spectroscopy. The series of the reacted cluster ions, Cu_nN^-, Cu_nNO^-, and CunNO^-₂ are observed in the mass spectrum. Photoelectron spectra are obtained at 3.49 eV photon energy for Cu_nN^- (n = 2 and 3) and Cu_nNO^-₂ (n = 1 and 2). The photoelectron spectrum of Cu₂N^- contains a band structure analogous to that of Cu^- or Cu₂. From the expansion gas pressure dependence of the band peak intensity in the spectrum, it is concluded that Cu₂N^- has at least two isomers in the beam. One of the isomers is expected to have a structure in which the central ion is Cu^- or Cu^-₂ and the residual atom(s) are weakly bound to the ion. For Cu_nNO^- (n = 1 - 3), we detected no electron signals with the detachment photon energy of 3.49 eV. The possible structure of CuNO^- is discussed in the light of the present results and also on the basis of the recent results of the study of CuO^-₂ by Wang and coworkers.