Charge separation in core excited argon clusters is reported. Neutral argon clusters have been prepared in a supersonic molecular beam. Photoionization with monochromatized synchrotron radiation in the L3/L2 regime (240–260 eV) initiates various single and double ionization processes. The photoion–photoion-coincidence (PIPICO) technique is applied to measure dissociative double ionization processes in core excited argon clusters. Three series of charge separation channels are observed: (i) Ar+/Ar+n, (ii) Ar+2/Ar+n, and (iii) Ar+3/Ar+n. Kinetic energy releases from charge separation reactions as well as the relative intensities of the PIPICO signals are discussed in relation to fragmentation mechanisms, resonant Auger spectra, and properties of cluster dications, such as cluster dication fragmentation energies and charge separation distances.

In aggregates of polymethine dyes the chromophores are tightly packed, causing strong intermolecular interactions, which lead to shifts of the absorption maxima. Thin layer aggregation (TLA) was used to form seven different polymorphs of a simple heptamethine dye in thin transparent films. It is demonstrated that large areas of uniform aggregate orientation can be achieved, yielding brilliantly colored spherulites, whose anisotropic absorption can be investigated directly in transmission by polarized UV/vis spectroscopy (see the inside front cover for an example).

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Core level excitation of weakly bonded atomic and molecular species is reported. Excitations into unoccupied orbitals with valence or Rydberg character as well as into the corresponding K-and L-continua are compared with the isolated and condensed species. Core level excitation of clusters is also accompanied with extensive fragmentation of singly and doubly charged clusters. Coincidence techniques such as photoelectronphotoion-coincidences (PEPICO) and photoion-photoion-coincidences (PIPICO) are used to study the photochemical fragmentation pathways of core excited clusters. Kinetic energy releases related to charge separation of cluster dications (Coulomb explosion) are derived from PIPICO spectra. The fragmentation energetics is discussed in relation to cluster dication threshold energies.