Multiphonon He atom scattering in He->Xe/Cu(111) collisions

We have investigated the collision between He-atoms and the xe(root 3x root 3)R30 degrees overlayer on Cu(111) under the conditions in which multiple phonons of the Einstein-like, vertically polarized Xe-vibration are excited and annihilated. The measurements are compared to theoretical results which were obtained using a recently developed formalism for calculating the multiphonon scattering spectra in the collision regimes in which both the motion of the scattered particle and surface vibrations must be treated quantum-mechanically. The energy and lateral momentum resolved scattering spectra are expressed in the form of a cumulant expansion in terms of uncorrelated and correlated phonon excitation amplitudes and the correlated ones can be neglected under the scattering conditions typical of He atom scattering. By introducing the one phonon interaction parameters into the obtained expressions we can calculate the multiphonon scattering spectra which are in a good agreement with the experimental data.