The agglomeration of copper or silver atoms in a matrix of noble gas atoms to form small clusters may be accompanied by the emission of visible light. Spectral analysis reveals the intermediate formation of electronically excited atoms and dimers as the source of the chemiluminescence. A mechanism is proposed, according to which the gain in binding energy upon cluster formation may even lead to the ejection of excited fragments as a result of unstable intermediate configurations. A similar concept was introduced in the field of nuclear reactions by Niels Bohr 60 years ago.

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Abstract. The surface plasmon absorption band of small Ag particles (diameter _< 100 A) in the gasphase as well as for clusters embedded in noble gas matrices is known to shift to higher energies and to broaden with decreasing diameter. This size effect depends sensitively on the microscopic surface properties of the clusters, which can be influenced by the interaction with the embedding matrix. Preovious experiments with silver clusters in the size range 20A < D _< 100A proved that for SiO2 and CO the matrix influence is strong enough to supersede the intrinsic size effect as observed in the noble gas matrices. The investigation of the i@uence of a CO matrix on smaller clusters with D < 20 A reveals a novel feature: the position as well as the width of the surface plasmon absorption band become independent of the cluster size,

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