QUANTUM EVAPORATION FROM SUPERFLUID-HELIUM SURFACES - OBLIQUE-INCIDENCE

We study the problem of surface scattering in (4)Helium at T = 0K. Sta rting with the microscopic superfluid theory of Beliaev [1] in a real space formulation [2] we derive an equation of motion for the quasipar ticles valid in bulk helium, through the surface and in the vacuum. Th is equation contains the physics necessary to calculate the different evaporation probabilities, and, in particular, the formalism retains t he diffuse nature of the surface of liquid helium and the non-locality of the helium-helium interaction. We solve the equation numerically a nd we present results for oblique incidence and for a range of quasipa rticle energies.