PREFERENTIAL SCATTERING OF AR FROM LIF - CORRELATION WITH LATTICE PROPERTIES

A study of the scattering of thermal energy Ar atoms from the (001) plane of LiF is reported. Multiple peaks in the scattered flux distribution are observed. The major peak in the distribution is the analog of the single lobe directed scattering distributions observed previously, using metal targets, in terms of its behavior as a function of angle of incidence and beam temperature. However, this major peak in the Ar/LiF data also displays a dependence on the azimuthal angle of the target which may be associated with the anisotropy in the elastic properties of LiF. Other peaks in the Ar distribution are observed to lie in fixed directions along rows of second-nearest-neighbor unlike ions in the LiF lattice. It is suggested that dipole-induced-dipole attractive forces serve to enhance the coupling of the Ar atoms to the longitudinal optical modes of vibration in these directions, giving rise to preferential re-emission.