Quasielastic helium atom scattering from a two-dimensional gas of Xe atomson Pt(111)

Quasielastic helium atom scattering provides direct evidence for a fully mo bile two-dimensional gas of Xe atoms on Pt(111) at a coverage of Theta(Xe) = 0.017 and a temperature of T-s = 105 K. Molecular dynamics simulations of the experimental data show that the frictional coupling rate between the X e atoms and substrate is less than 0.25 ps(-1) and the lateral potential co rrugation for single Xe atoms is less than 9.6 meV, which is only 40% of th e value previously determined at high coverage.