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Abstract

The vibrational spectra of Ag₃ and Ag₄ are recorded in the far-infrared between 100 and 220 cm^-1 using multiple photon dissociation spectroscopy of their complexes with Ar atoms. For Ag₃-Ar two IR active bands are found at 113 and 183 cm^-1, for Ag₄-Ar one band at 163 cm^-1 and very weak IR activity at 193 cm^-1 are observed. This, together with recent theoretical studies, allows for a reassignment of the controversial vibrational data reported earlier for the bare Ag₃ cluster. The influence of the number of Ar atoms in the complexes on the frequency of the IR active modes is found to be minor. However, the low-frequency IR-active band of Ag₃ shifts with increasing Ar coverage from 113 cm^-1 for Ag₃-Ar to about 120 cm^-1 for Ag₃-Ar₄, the value known for Ag₃ embedded in rare gas matrices.