High frequency capillary waves on a liquid Gallium surface were studied by quasi-elastic light scattering spectroscopy. The observed damping constants of the waves differ greatly from the predictions of classical theoretical treatment of the surface as that of a simple Liquid. This is explained in terms of the presence of a surface layer possessing visco-elastic properties which are extracted from the fit of experimental spectra using different theoretical forms. One of the mast important results of the data analysis is that the surface dilational viscosity appears to be negative. This result implies that the widely used phenomenological theoretical model should be replaced by one taking into account processes of adsorption and diffusion.