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.

• Received 9 March 1992

DOI:https://doi.org/10.1103/PhysRevB.46.575