EFFECT OF CORRELATED FLIGHTS ON PARTICLE MOBILITIES DURING SINGLE-FILE DIFFUSION

When large adsorbates diffuse in the pores of zeolites and molecular s ieves, they can undergo single-file diffusion. The mean-square displac ement of particles during single-file diffusion, [x(2)(t)], is proport ional to t(1/2). By contrast, in the absence of other particles, an is olated adsorbate will perform normal diffusion with a tracer diffusion coefficient D-0. An important goal of theoretical treatments of singl e-file diffusion is to relate D-0 and the single-file mobility, F=[x(2 )(t)]/2t(1/2). One physical feature that is ubiquitous in activated di ffusion in periodic potentials, such as the diffusion of adsorbates in zeolites, is the appearance at sufficiently high temperatures of corr elated flights that pass through multiple binding sites. We show that when isolated particles can perform multisite flights, the expression usually used to relate D-0 and F is not exact, and we investigate meth ods that can lead to more accurate expressions. We discuss how the exi stence of long flights affects equilibrium adsorbate structures and co mment on the implications of our results for the interpretation of exp erimental measurements of single-file diffusion.