Theoretical studies of atom-solid elastic scattering: He+LiF

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Abstract
The elastic scattering of an atom from a solid surface is considered in the close-coupling formulation. The resulting sets of coupled differential equations are solved by a technique developed by Gordon and previously applied to atom-molecule inelastic scattering. For the example of He+LiF, utilizing the Lennard-Jones, Devonshire model potential, it is shown that basis sets consisting of only low order diffraction channels can be seriously in error. Results are presented using typically 29 coupled channels but as many as 41 channels are included for individual cases. Several calculations including only five coupled channels are also presented. These results are shown to be very useful in interpreting the causes of various effects seen in the 29 channel computations even though providing a poor over-all approximation to the 29 channel results. Various diffraction processes (with emphasis on the specular intensity) are studied as functions of the coupling between the specular and diffracted beams, the incident direction, and for the two isotopes He3, He4. The direct numerical approach used here automatically includes the effect of bound state resonances. These are seen to have a significant effect on the specular intensity. This is found to be the usual behavior at the threshold for the first nonspecular channel, but can also occur when there are already many channels open. Many of the trends observed in experimental data are also observed in the present results.