ANOMALOUS DIFFUSION AT LIQUID SURFACES

We study the role of bulk-surface exchange in the diffusion of adsorbed molecules at liquid-solid and liquid-fluid interfaces. For strong adsorbers (readsorption time much less than desorption time) we find anomalous surface diffusion on time scales less than the surface retention time: Displacement moments grow as rqt (q), where (q)=q for q<1, (q)=(q+1)/2 for q>1, and r tlnt. This superdiffusive behavior arises because molecules execute Lévy walks on the surface, mediated by the liquid bulk. © 1995 The American Physical Society.