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The reaction of oxygen with Cu cluster anions consisting of 6-11 atoms was studied by means of Time-of-Flight mass (TOF) spectroscopy and Ultraviolet Photoelectron Spectroscopy (UPS). Using molec- ular oxygen, we found that a Cucluster (n =6 −11) can react only with one single oxygen molecule, which adsorbs molecularly, implying that the clusters studied here are less reactive towards oxygen chemisorption compared to the smaller clusters ( n< 5). This result indicates that chemical properties can alter signifi- cantly with increasing cluster size. Depending on the cluster source conditions, different cluster structures and reactivity patterns were found. These results are used to qualitatively describe the chemisorption energetics of oxygen on Cu cluster anions. PACS. 33.60.Cv Ultraviolet and vacuum ultraviolet photoelectron spectra - 36.40.Jn Reactivity of clusters - 36.40.Mr Spectroscopy and geometrical structure of clusters - 36.40.Wa Charged clusters

Using a new experimental setup we have measured UV (h ν = 6.4 eV) photoelectron spectra of cold silicon cluster anions Si n - in a very broad size range. For sizes up to n = 46 the spectra exhibit rich structures. For larger sizes only smooth spectra have been obtained. No trace of a bandgap has been found even for clusters with more than 1000 atoms.

Copper cluster anions in the size range of 1-18 atoms are studied by photoelectron spectroscopy. Using photons of 5.0 eV energy the electronic level structure built from the delocalized s-orbitals of the atoms is revealed. An attempt is made to assign the observed bands to the electronic shells predicted by the jellium model. Even though the general behavior resembles the predictions of this model, the spectra are much more complicated reflecting the discrete atomic geometry of these particles.

Photoelectrons from mass-identified jet-cooled tin and lead cluster anions (Sn n , Pb n ) are detached by ultraviolet laser light (hngr=3.68 eV). The photoelectron energy spectra give the detachment energies of ground state cluster anions (electron affinities) as well as excitation energies of neutral clusters in the geometry of the anions. The energy spectra for Sn n are dominated by flat thresholds with ann-dependence similar to that of other group IV clusters. In contrast, for Pb n we find pronounced narrow lines close to threshold, generally followed by a 0.3 1.4 eV gap which indicates closed-shell behaviour of Pb n for nearly alln.

Aluminium cluster anions (Al n ) are produced by laser vaporization without additional ionization and cooled by supersonic expansion. Photoelectrons from mass-identified anion bunches (n=2...25) are detached by laser light (hv=3.68 eV) and undergo energy analysis in a magnetic bottle-type time-of-flight spectrometer. The measurements provide information about the electronic excitation energies from ionic ground states to neutral states of the clusters. In contrast to bulk aluminium these cluster photoelectron spectra partially have well-resolved bands which originate from low-lying excited bands. For small clusters, especially the aluminium dimer and trimer, quantum-chemical calculations will be compared to the measurements. The electron affinity size dependence of larger clusters shows conclusive evidence for "shell" effects.