Exploring single-file diffusion in one-dimensional nanochannels by laser-polarized Xe-129 NMR spectroscopy

Single-file diffusion behavior is expected for atoms and molecules in one-d imensional gas phases of nanochannels with transverse dimensions that do no t allow for the particles to bypass each other. Although single-file diffus ion may play an important role in a wide range of industrial catalytic, geo logic, and biological processes, experimental evidence is scarce despite th e fact that the dynamics differ substantially from ordinary diffusion. We d emonstrate the application of continuous-flow laser-polarized Xe-129 NMR sp ectroscopy for the study of gas transport into the effectively one-dimensio nal channels of a microporous material. The novel methodology makes it poss ible to monitor diffusion over a time scale of tens of seconds, often inacc essible by conventional NMR experiments. The technique can also be applied to systems with very small mobility factors or diffusion constants that are difficult to determine by currently available methods for diffusion measur ement. Experiments using xenon in nanochannel systems can distinguish betwe en unidirectional diffusion and single-file diffusion. The experimental obs ervations indicate that single-file behavior for xenon in an organic nanoch annel is persistent even at long diffusion times of over tens of seconds. F inally;using continuous flow laser-polarized Xe-129 NMR spectroscopy, we de scribe an intriguing correlation between the observed NMR line shape of xen on within the nanochannels and the gas transport into these channels.