Experimental Study on Creation and Decay Processes of Excitons in Rare Gas Clusters

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During the term of this project, we have designed and constructed and apparatus for the study of the electronic excitation processes in rare-gas clusters using the electron energy loss spectroscopy, and have obtained some preliminary results for the excitonic excitation process in Kr cluster. The experimental setup consists of a vacuum chamber including a pumping system, an electron energy loss spectrometer, 2 types of supersonic cluster beam source, and a cluster ion detector for the measurement of the cluster size distribution.Using the cluster beam source using a differential cryo pumping system, we have measured the electron energy loss spectra for Kr_n cluster (n=500-600), at the electron impact energy of 100eV and the observation angle of 0 deg. Creation of the surface excition in the cluster, which corresponds to the excitation of 4p^55s state in an isolated atom, has been clearly observed.Our plan from the next year is as follows,(1) Measurement of the excitonic excitation spectra for Ne and Ar clusters using a conventional type cluster beam source, which has been constructed recently.(2) Confirmation of the existence of stable negatively charged Kr and Xe clusters, whose electron affinities are known to be negative in atoms, and positive in solids, which suggests the change of the sign of electron affinity in clusters.