Molecular transport in subnanometer channels

The density functional method is used to show that the description of molec ular transport in subnanometer channels reduces to the description of diffu sion in a one-dimensional system where strong density fluctuations with a f inite cluster lifetime. A new diffusion mechanism is proposed; it makes it possible to explain the transition from activated diffusion of single parti cles in a channel at a low filling factor to fast barrier-free diffusion, w hich consists of the propagation of density disturbances at high filling fa ctor. It is shown that as the filling factor increases, the attraction betw een the molecules (the effective attraction of molecules-hard spheres) caus es the energy barrier for diffusion along the channel axis to vanish. Anoth er consequence of the "effective" attraction between the molecules is the f ormation of molecular clusters in the channel, which possess a finite lifet ime because of the one-dimensionality of the system. The size and lifetime of the clusters increase with the filling factor of the channel. The diffus ion of particles in clusters is a barrier-free process of propagation of de nsity disturbances. The dependences obtained for the diffusion coefficient on the pressure, temperature, and filling factor make it possible to descri be, even in the hard-sphere model, all experimental data known to the autho rs. (C) 2000 MAIK "Nauka / Interperiodica".