On the Debye-Waller factor in molecular beam scattering experiments

In the molecular beam scattering experiments against metal surfaces, one often obtains surface Debye temperatures larger than the bulk ones, in apparent contradiction to the larger thermal atomic motion at the surface. We point out that this is a consequence of that the thermal molecules scatter against the outer part of the electron distribution, and that the metal electrons do not follow the atomic motion rigidly. A self-consistent model calculation shows that this is a large enough effect to explain the experimental results.