No abstract

Core level photoelectron and x-ray absorption spectra for free argon clusters from (N) = 5 to (N) = 4000 are presented. Spectral features originating from surface and bulk sites of the clusters are identified. These are seen to shift with cluster size. From the development of the spectra from the isolated atom to the largest clusters, information about both the size-dependent cluster-specific electronic structure and that of the "infinite" solid is obtained. Using a simple model for the core level binding energy shifts, effective surface coordination numbers are derived. These range from 5.3 for (N) = 10 to 8.5 for the solid. PACS numbers: 73.61.Ng, 36.40.c, 78.70.Dm, 79.60.Bm Clusters can be seen as polyatornic aggregates between isolated atoms and bulk solids, in which a considerable part of the atoms are located in surface sites of low coordination numbers [1 -3]. The nature and distribution of

Spin polarized photoemission studies of the 3s core level in ferromagnetic systems (abstract) Photoelectron spectra of the argon 2 p core level for free argon clusters of up to 4000 atoms are compared to detailed calculations. The comparison shows that the size-dependent shifts of the core level binding energy can be explained in a pure polarization-screening model. Important differences arise between the shifts for the bulk ͑interior͒ and the surface atoms. The agreement between experiment and theory allows the extrapolation of the cluster data to the ''infinite'' solid. In this way we obtain the shifts of the core level binding energy between the free atom, the surface atom and the bulk of argon. The relation between these shifts and those of the first ionization potential is discussed.

Core level x-ray absorption and photoemission spectra of free water clusters are presented. Core and valence photoemission spectra show a weak but gradual change with cluster size. Comparisons to spectra of the isolated molecule and solid ice indicate that water molecules have a lower average coordination in clusters than in the bulk solid. X-ray absorption spectra reveal spectral characteristics between the free molecule and the bulk. These are compared to similar spectra of the isolated molecule and solid ice, and discussed in connection to calculated structures.

The first highly resolved electronic spectra of small non-alkali metal clusters embedded in nanoscopic helium droplets (N ≈ 20 000) are presented. The helium droplets serve as an extremely cold liquid matrix with a temperature of 0.37 K. Resonant two-photon-ionization is used for size-selective spectroscopy on a silver cluster distribution (N ≤ 10). Results are reported for Ag 2 , Ag 3 and for Ag 8 . For the latter, a very narrow absorption spectrum is resolved corresponding to the Ag 8 plasmon resonance. The linewidth of the observed resonance is a factor of two smaller than theoretical zero-temperature predictions for the plasmon line width of closed-shell metal clusters. In contrast, the lifetime of the Ag 8 resonance is estimated to be of the order of nanoseconds, which is inconsistent with the plasmon picture and typical for molecular transitions.PACS. 36.40.Mr Spectroscopy of clusters -67.40.Yv Impurities and other defects in 4 He