Aggregation of small CsI clusters inside Ar clusters: ionization and fragmentation under soft X-ray excitation

Medium size Ar clusters ∼500 were used to pick-up and aggregate CsI molecules. The primary Ar cluster beam can be converted into a beam of bare or Ar-covered alkali halide clusters by varying the number of pick-up events. Soft X-ray photoionisation was used to monitor the depletion of the Ar shell around the guest cluster. It was found that the Ar coverage controls the mechanism and degree of guest cluster ionization. For embedded CsI clusters charge transfer from the Ar shell is the dominant soft X-ray ionization process. Small alkali halide cluster fragments are ejected from the Ar host cluster. The detection of weakly bound stoichiometric (CsI)n+ clusters indicates that the Ar-shell prevents the desorption of neutral halogen atoms

Innershell photoionisation spectroscopy of NaCl clusters

X-ray absorption near edge spectroscopy (XANES) was used to investigate the size dependent development of XANES structures from free molecules and clusters up to the solid NaCl. For measurements on clusters a new type of cluster source was designed in order to provide an intense and continuous cluster beam for inner shell absorption experiments on tightly bound clusters. Partial ion yield absorption spectra at the Cl 2p-edge were recorded for different NanCln−1 ions using a time-of-flight mass spectrometer at the high flux and high resolution undulator beamline BW3 at HASYLAB. The absorption spectra revealed a gradual evolution from the NaCl molecule and cluster to the solid. A comparison with recently performed multiscattering calculations indicates that the bond length even for rather small clusters (n=4) is increased by approximately 50% of the bond length change from the molecule to the solid

Observation of small metastable multiply charged CsI clusters embedded inside rare gas clusters

Medium size Kr and Ar clusters ∼200-400 were used to pick up and aggregate CsI molecules. By varying the number of pick-up events it was possible to change the size of the guest cluster and the thickness of the rare gas coverage around the alkali halide cluster. “Soft” single (multiple) ionisation of the alkali halide core was achieved via charge transfer from the primary ionised rare gas shell. It turns out that the rare gas shell controls the vibrational relaxation of CsI cluster ions. Due to cooling by the rare gas shell shallow metastable states of multiply charged CsI clusters can be populated and detected. Clusters as small as Cs5I32+, Cs6I52+, Cs13I133+ and Cs17I143+ could be observed for the first time. The abundance of these multiply charged clusters steeply decreases if the thickness of rare gas shell shrinks