Optical absorption of small copper clusters in neon: Cun, (n=1-9)

We present optical absorption spectra in the UV-visible range (1.6 eV < <(h)over bar>omega < 5.5 eV) of mass selected neutral copper clusters Cu-n(n = 1-9) embedded in a solid neon matrix at 7 K. The atom and the dimer have already been measured in neon matrices, while the absorption spectra for sizes between Cu-3 and Cu-9 are entirely (n = 6-9) or in great part new. They show a higher complexity and a larger number of transitions distributed over the whole energy range compared to similar sizes of silver clusters. The experimental spectra are compared to the time dependent density functional theory (TD-DFT) implemented in the TURBOMOLE package. The analysis indicates that for energies larger than 3 eV the transitions are mainly issued from d-type states; however, the TD-DFT scheme does not reproduce well the detailed structure of the absorption spectra. Below 3 eV the agreement for transitions issued from s-type states is better. (C) 2011 American Institute of Physics. [doi:10.1063/1.3552077]