Multiphonon energy transfer in atom-surface scattering

The probability density P(ω,q) of transferring the energy ω and the parallel momentum q to the surface is determined by the maximum entropy subject to constraints procedure. The two important constraints are identified as the recoil energy and the mean parallel energy transfer. Having determined P(ω,q) one can evaluate all observable quantities, e.g., the triple differential reflection probability d³σ/dE_tdΩ or the trapping probability. A three-parameter model for d³σ/dE_tdΩ is derived by assuming a parameterized form for the recoil energy. This model may be regarded as an extension of the hard-cube model, because it reduces to the latter if the third parameter, the speed of sound c, is set to infinity. The comparison of the predicted velocity and angular distributions with recent experiments of Hurst et al. is excellent considering the simplicity of the model.