Quasi-elastic He atom scattering measurements had provided clear evidence for a 2-dimensional free gas of Xe atoms on Pt(111) at low coverages. Increasing the friction due to the surface, a gradual change in the shape of the quasi-elastic peak was predicted and analyzed in terms of the so-called motional narrowing effect. This type of analysis of the quasi-elastic peak was recommended to precede

deconvolution, the better to extract information (diffusion coefficients, jump distributions) from the process. This analysis also predicted conditions, for the free gas regime, which were different to those reported previously.

Quasi-Elastic Peak Lineshapes in Adsorbate Diffusion on Nearly Flat Surfaces at Low Coverages - the Motional Narrowing Effect in Xe on Pt(111). R.Martínez-Casado, J.L.Vega, A.S.Sanz, S.Miret-Artés: Journal of Physics - Condensed Matter, 2007, 19[17], 176006 (8pp)