Inner-shell excitation of clusters

Photoionization of clusters in the regime of valence electron excitation has provided in the past information on ionization potentials, thermochemical and spectroscopic properties as a function of cluster size. More recently, core level excitation with soft x-rays has been investigated in order to bridge the gap between spectroscopic and photochemical properties of the isolated gas phase species and the condensed phase. First systems under investigation have been rare gas clusters, and aggregates of simple molecules. This paper reports size-dependent properties of clusters occurring in the inner-shell excitation regime. These include (i) changes in spectroscopic properties in the near-edge (NEXAFS) regime as well as in the corresponding ionization continua, where extended x-ray absorption fine structure (EXAFS) is observed; (ii) shifts of the core ionization energies; (iii) radiative relaxation processes, and (iv) fragmentation of multiply charged clusters, which are formed after electronic and radiative relaxation, via charge separation ('Coulomb explosion'). (author)