HE-4 ATOMS INCIDENT ON A SUPERFLUID HE-4 SLAB - QUANTUM STICKING, SCATTERING AND TRANSMISSION

We present the results of a microscopic theory of the scattering, tran smission, and sticking of He-4 atoms impinging on a zero temperature H e-4 slab at near normal incidence. The theory includes coupling betwee n different modes and allows for inelastic processes. The present work focuses on the elastic reflection and transmission of a 4He atom in t he sense that we examine these intensities for atoms which have the sa me energy as the incident atoms. We find a considerable loss of total intensity due to scattering into multiple excitations. The reflected s ignal is in qualitative and semi-quantitative agreement with experimen tal results for 4He atoms scattered from the surface of bulk helium. T he transmission intensity - which has not been measured - shows a very strong energy dependence. Moreover, we show that this dependence is s ubstantially different from the Feynman level theory, which doesn't pe rmit the decay of the single excitation into multiple excitations, and thus cannot describe a reduction in total intensity. In our theory, t he major source of decay of elastic transmission and reflection (i.e., sticking) is from the production of ripplons at the liquid-vacuum int erfaces.