Surface Vibrations from Small Clusters to the Solid: He Atom Scattering fromArn

In a crossed molecular beam arrangement helium atoms are scattered from argon clusters which are generated in the size range of $\overline{n}=25\mathrm{}$ to $\overline{n}=4600\mathrm{}$ by adiabatic expansion with conical nozzles. The inelastic energy transfer is detected by time-of-flight analysis of the scattered helium atoms with a resolution of better than 1 meV. The measured peak of the transferred energy is attributed to surface vibrations. It decreases as a function of the average cluster size and converges to the value of the surface phonons of solid argon.