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

The electronic properties of copper cyanide cluster anions [Cu-n(CN)(m)(-); n=1-6, m=1-6] were studied using photoelectron spectroscopy (PES) with a m agnetic-bottle type electron spectrometer. Both the anions and the cations of the Cu-n(CN)(m) cluster were generated by laser vaporization of a molded copper cyanide rod in a He carrier gas. In the mass spectra, abundant clus ters were produced at the composition of (n,m)=(n,n+1;n=1-6) and (n,n;n=4 a nd 5) for the anions, whereas more abundant clusters were observed at (n, n -1; n=1-9) for the cations. The stability of Cu-n(CN)(n+1)(-) and Cu-n(CN)( n-1)(+) clusters is attributed to their electronic structure, where ionic C u+ and CN- are linked alternately in a linear geometry. The PES spectra of the Cu-n(CN)(m)(-) anions show that the (n,n+1) clusters exhibit an extreme ly large EA of above 4.5 eV, while the EA's of the less abundant (n,n) clus ters 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 d ensity functional theory (DFT), two different linear isomers have been foun d for (n,n) clusters, where CN takes a opposite direction toward Cu. For Cu -4(CN)(4)(-) and Cu-5(CN)(5)(-), moreover, the PES spectra show two compone nts of distinctly different peak shape, suggesting that a ring isomer shoul d coexist with the linear ones. (C) 2000 American Institute of Physics. [S0 021- 9606(00)00429-3].