Photoelectron spectroscopy of copper cyanide cluster anions: On the possibility of linear and ring structures

Abstract

The electronic properties of copper cyanide cluster anions [Cun(CN)m−; n=1–6, m=1–6] were studied using photoelectron spectroscopy (PES) with a magnetic-bottle type electron spectrometer. Both the anions and the cations of the Cun(CN)m cluster were generated by laser vaporization of a molded copper cyanide rod in a He carrier gas. In the mass spectra, abundant clusters were produced at the composition of (n,m)=(n,n+1;n=1−6) and (n,n;n=4 and 5) for the anions, whereas more abundant clusters were observed at (n, n−1; n=1−9) for the cations. The stability of Cun(CN)n+1− and Cun(CN)n−1+ clusters is attributed to their electronic structure, where ionic Cu+ and CN− are linked alternately in a linear geometry. The PES spectra of the Cun(CN)m− anions show that the (n,n+1) clusters exhibit an extremely large EA of above 4.5 eV, while the EA’s of the less abundant (n,n) clusters increase monotonously with cluster size from 1.3 eV (n=1) to 3.12 eV (n=6), except for n=4 and 5. Together with theoretical calculations by the density functional theory (DFT), two different linear isomers have been found for (n,n) clusters, where CN takes a opposite direction toward Cu. For Cu4(CN)4− and Cu5(CN)5−, moreover, the PES spectra show two components of distinctly different peak shape, suggesting that a ring isomer should coexist with the linear ones.