Angular Distribution of Scattered and Desorbed Atoms from Specular Surfaces

摘要

The angular distribution of atoms and molecules leaving a cleavedhyphen;crystal surface, on which the conditions for specular reflection are fulfilled, is analyzed. Starting from published experimental data concerning the reflecting power vs glancinghyphen;angle dependence (Hendash;LiF system) and from some general considerations, the existence of a deviation from the cosine law of the angular distribution of atoms, leaving a specular surface after an inelastic collision, is pointed out. It is shown that this deviation is correlated with the shape of the reflecting power vs glancinghyphen;angle curve, belonging to the atoms which undergo a specular reflection on this surface. A tentative model for the specular reflection of helium on LiF cleavedhyphen;crystal surfaces is proposed; it considers, in analogy with the neutron case, the specular reflection of atoms as total reflection on a surface of positive average interaction potential. The proposed model leads to a reflecting power vs glancinghyphen;angle curve which fits rather well the experimental data. Moreover, it explains qualitatively the correlation between the shape of the reflecting power vs glancinghyphen;angle curve and the characteristics of the deviation from the cosine law of the angular distribution for atoms having undergone an inelastic collision. Experiments for the checkhyphen;up of the general conclusions, as well as of the tentative model, are proposed.