Quasielastic Helium Atom Scattering from a Two-Dimensional Gas of Xe Atoms on Pt(111)

Quasielastic helium atom scattering provides direct evidence for a fully mobile two-dimensional gas of Xe atoms on Pt(111) at a coverage of ${\Theta }_{\mathrm{Xe}}=0.017\mathrm{}$ and a temperature of $T_s=105\mathrm{}\mathrm{K}$. Molecular dynamics simulations of the experimental data show that the frictional coupling rate between the Xe atoms and substrate is less than $0.25{\mathrm{ps}}^{-1\mathrm{}}$ and the lateral potential corrugation for single Xe atoms is less than 9.6 meV, which is only $40\%$ of the value previously determined at high coverage.