OPTICAL-RESPONSE OF CESIUM COATED C-60

Photoabsorption spectra are reported for Cs and C60Csn+ clusters for n =40, 60, 120 and 310. The spectra were obtained by heating the mass se lected clusters in a beam by means of photoabsorption until they evapo rated metal atoms. The resulting mass loss was observed in a time-of-f light mass spectometer. The plasmon-like resonance in pure Cs clusters shifts to lower energies with decreasing cluster size. The collective electronic excitations in clusters containing C-60 are Split in energ y as would be expected for fullerene molecules coated with layers of m etal.