SCATTERING OF HE-3 AND HE-4 ATOMS FROM HE-4 CLUSTERS

We develop a microscopic theory of elastic and inelastic scattering an d sticking of He-3 and He-4 atoms impinging on superfluid He-4 cluster s. A number of essential aspects must be observed in a physically mean ingful and reliable theory of such scattering processes. These are all connected with multiparticle processes, particularly the possibility of energy loss. These processes are (a) the coupling to low-lying exci tations which is manifested in a finite imaginary part of the self ene rgy, (b) the interaction with roton-like excitations and the broadenin g of the roton minimum due to finite-size effects, and (c) the discret eness of low-lying excitations in helium clusters.