Photoelectron Spectroscopy on Small Anionic Copper-Carbonyl Clusters

Anion photoelectron spectroscopy in combination with density functional theory (DFT) calculations has been used to study mono- and dinuclear copper-carbonyl clusters Cun(CO)m- (n = 1, 2; m = 2-5). The adiabatic detachment energies of the anions have been measured which correspond to the electron affinities of the respective neutral species. The corresponding values are 0.95 eV for Cu(CO)2, 1.02 eV for Cu(CO)3, 1.04 eV for Cu(CO)4, 1.43 eV for Cu2(CO)4, and 1.19 eV for Cu2(CO)5. All spectra exhibit a pronounced vibrational fine structure on the adiabatic photodetachment peak. The energy splitting is close to the energy of the C-O stretching vibration of the neutral cluster (final state). The DFT calculations clearly indicate that in all clusters the highest occupied molecular orbital (HOMO) is a CO-derived π* orbital. Furthermore the calculations are used to give insight into geometry, frontier orbitals, vibrational frequencies and spin multiplicity of the neutral and anionic clusters.