The influence of CO on the surface plasmon absorption band of small silver clusters (D<=20 angstrom)

The surface plasmon absorption band of small Ag particles (diameter less than or equal to 100 Angstrom) 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. Previous experiments with silver clusters in the size range 20 Angstrom less than or equal to D less than or equal to 100 Angstrom 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 influence of a CO matrix on smaller clusters with D less than or equal to 20 Angstrom reveals a novel feature: the position as well as the width of the surface plasmon absorption band become independent of the cluster size.