IMPACT COLLISION ION-SCATTERING SPECTROSCOPY AT LARGE INCIDENCE ANGLES AS A METHOD FOR STUDYING RARE-GAS ADSORPTION

Energy spectra of ions emitted from the cold (100) nickel surface cove red by a krypton or argon condensed layer under 5 keV Ne+ ion bombardm ent were measured for chosen values of the incidence angles. The depen dence of the intensity of single-scattering peaks for nickel and adsor bed atoms on the incidence angle was especially examined in the region of large incidence angles. In this region some structure of the inten sity curves can be connected with scattering by so-called ''subsurface '' atomic pairs (the scattering atom lies deeper than the shadowing at om). It is shown that such structure allows one to find the distance b etween the first adsorbed atomic layer and the topmost atomic layer of the substrate. This distance for the krypton adsorption (3.5 +/- 0.8 angstrom) is about two times more than for the argon adsorption (1.6 /- 0.5 angstrom). This means that the argon adsorption has a more comp lex character than the krypton adsorption which, independent of ion bo mbardment, remains as a physical (van der Waals) adsorption.