Surface energy of liquid hydrogen with adsorbed helium

The binding energy of helium to the surface of liquid hydrogen has been determined by measuring the surface energy of liquid hydrogen in the presence of helium gas. From the linear dependence of the surface energy on the density of helium gas the binding energy is found to be 16±2 K. The variation of the surface energy at higher densities cannot be explained in terms of simple extensions of a single-particle description of the binding of He to the ${\mathrm{H}}_2$ surface.