| Abstract
| - We study the tracer exchange of molecules between the phase adsorbed in one-dimensional channels and thesurrounding gas phase by molecular dynamics simulations. Under the conditions of single-file diffusion, anovel boundary effect is observed. The shape of the tracer-exchange concentration profiles deviates fromthose obtained under the conditions of normal diffusion. Compared to the profiles for normal diffusion, whichcorrespond to the same degree of exchange, the equilibrium concentration is reached faster at the boundariesand slower in the middle part of the channel in the case of single-file diffusion. This boundary effect isobserved for the system neopentane in AlPO4-5 (which was chosen as a reference system), as well as formodified systems. The effect can be understood considering two diffusion mechanisms which occur in parallel.First, the diffusion of the whole chain of particles, that is, the center-of-mass diffusion, obeying the laws ofnormal diffusion. Second, the individual movement of the particles relative to the center of mass of thechain. The second mechanism admits additional displacements which, on average, lead to an acceleratedexchange of the marginal particles.
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