The adsorption of xenon on a thick crystalline ice layer grown in situ on a Pt(111) substrate has been investigated with high resolution helium atom scattering. The dependence of the specular reflectivity during xenon adsorption and desorption reveals a phase that desorbs at 50.5 K, which is thought to correspond to a single monolayer, and a lower coverage 0.25 monolayer phase with a desorption temperature of 53 K. Both phases exhibit (1x1) helium diffraction peaks. Time-of-flight spectra reveal perpendicular vibrational frequencies of homega=2.5 meV for both phases and an additional 2.0 meV mode for the monolayer phase. (C) 2003 American Institute of Physics.