Atom scattering at 4He droplets

We present theoretical calculations of the structure and excitations of helium clusters. Our calculations include the multi-particle excitations and lifetime effects and, thus, bring the description to a level that is comparable to the one previously reached only in the bulk liquid. We calculate both the low-lying, discrete excitations and the dynamic structure function and demonstrate that it shows strength for both, a phonon-roton branch and a ripplon branch. Equipped with a plausible description of the pure droplets, we then consider 3He impurities and their excitations, and finally the scattering of 4He and 3He off 4He droplets and determine the dependence of scattering cross sections on the energy and the particle species