One-phonon and multiphonon processes in atom-surface scattering

We show that previously unexplained features in the TOF spectra of He and Ne scattered from solid surfaces can be attributed to multiphonon processes. We find that a simple Gaussian distribution, obtained by Brako and Newns within the trajectory approximation, accounts rather well for these features. The average energy transfer appearing in this distribution is evaluated by the Baule formula. We obtain an interpolation formula that describes both multiphonon and one-phonon processes, and is consistent with the Distorted Wave Born Approximation for the latter.