ENERGY-TRANSFER BETWEEN RIPPLONS AND PHONONS IN LIQUID-HELIUM AT LOW-TEMPERATURES

We discuss the energy transfer between ripplons and phonons in liquid helium at temperatures T < 1 K. The dominant process proves to be one wherein a phonon incident on the liquid surface is completely absorbed with the emission of two ripplons. The inelastic scattering of a phonon from the surface is found to be less effective. The thermal contact between ripplons and phonons is very poor at low temperatures; below 0.1 K it is worse than that between bulk helium and copper. This can have serious consequences for experiments on atomic hydrogen.