Quantum quasiresonances in grazing incident angle atom-surface   collisions
  The momentum transfer between the normal components to an index direction in the collision of an atom with a periodic surface is investigated. For fast atoms with grazing angle of incidence there is an interval of azimuthal angles around the index direction for which the energy transfer can be very efficient. This effect is reflected in quantum diffraction patterns with large non-specular peaks, associated with the parallel to the surface and normal to the index direction momentum component, and can be described in terms of quasiresonance. Although the classical dynamics does not reproduce the precise quantum diffraction probabilities, indicating the quantum nature of this effect, classical and quantum computations show that the span of the quasiresonance region coincides in both dynamics and can be classically estimated from the phase-space analysis. 
Antonia Ruiz, Jose P. Palao, and Eric J. Heller