Reflection ofHe4Atomic Beams from Clean LiF Surfaces

Abstract
We have studied reflection of a He4 nozzle beam from a LiF crystal surface cleaved in situ at 109 Torr. As compared with previous results on water-covered surfaces, the selective adsorption intensity minima are pronouncedly sharpened and deepened and there is considerable fine structure. The main minima can be associated with three bound states and two positive-energy resonances. On aging the surface in the vacuum, the fine structure fades and the bound-state energy levels shift slightly.