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.