7.1.2.2 Semi-empirical atom-surface potentials

This chapter discusses kinematics and resonant scattering, semi-empirical atom-surface potentials. The kinematic parameters of elastic scattering are provided. The intensity of the diffracted beams, including the specular, as a function of ε₁ or of the incidence angles, often displays sharp features, including isolated minima (selective adsorption) and maxima. All beams are affected for the same conditions of incidence, which suggests that a resonance process is involved. At resonance, an atom is trapped in a surface-bound state for times of the order of 10^-12 seconds. For a molecule, it is also possible to have resonances mediated by a rotational excitation. A general expansion of the static potential, which comes naturally for coupled channels calculations, is given.