SELECTIVE ADSORPTION RESONANCES AT RAINBOW CONDITIONS IN THE SCATTERING OF ATOMS BY STEPPED SURFACES - APPLICATION TO THE HE-4 CU(117) SYSTEM/

For stepped surfaces, dynamics is not parity reversal invariant with r espect to the step configuration and the way the atomic beam approache s the surface, downstairs or upstairs scattering, should dramatically change rainbow patterns. We show that only one close-coupling calculat ion provides us information of the two possible scatterings at once. F urthermore, it is possible to find some incident conditions where surf ace rainbow is displayed for both configurations. At the same time, if resonances are analysed at rainbow conditions, we could enhance reson ant features in the diffraction channel displaying rainbow. An applica tion to the study of diffraction of He-4 atoms by the Cu(117) surface is presented.