Probing the (dual) repulsive wall in the interaction of O2, N2 and Ar with the Ag(111) surface

We have performed molecular beam scattering experiments of O₂,N₂, and Ar from the Ag(111) surface in the translational energy regime from 0.2 to 2.6 eV and at surface temperatures of 600 and 150 K. The experiments were carried out to probe the repulsive part in the particle-surface interaction potential. It is shown that the scattering dynamics of the systems N2-Ag(111) and Ar-Ag(111) is characteristic of physisorption systems. The scattering data for the system O₂-Ag(111) shows that both the physisorption and chemisorption part of the interaction potential are probed in the experiment. For "normal incidence energies" exceeding a threshold energy, the barrier to the chemisorption part of the interaction potential can be crossed. An upper limit for this threshold is Ei cos² q_i=0.3 eV. Although the chemisorption region is probed, the (dissociative and nondissociative) chemisorption probability remains negligible.