Diffraction and rainbows in the scattering of argon from 2H-W(100)

We observe clearly resolved diffraction peaks in the scattering of argon from a 2H-W(100) surface, demonstrating the importance of quantum effects even for relatively heavy atoms. The argon diffraction peak intensities decrease exponentially with substrate temperature in a manner consistent with a surface Debye temperature of ~ 400 K. For large incidence angles, (e.g. θi = 60°), angular distributions are observed to consist of a single quasi-specular lobe which narrows substantially with incidence energy. In contrast, for θi = 30°, a rainbow distribution is found with the angular separation of the two lobes decreasing with increasing energy. These observations are discussed in terms of classical and quantum models of gas-surface scattering. © 1991.