ANOMALOUS HELIUM-GAS-INDUCED SPIN-LATTICE RELAXATION AND THE EVIDENCEFOR ULTRA MICROPORES IN MICROPOROUS CARBON

The spin-lattice relaxation mechanism of dangling bond spins in activa ted carbon fibers (ACF) with huge specific surface areas (similar to 3 000m(2)/g) was investigated by ESR measurements in the presence of the gases, He, Ne, Ar, H-2, N-2, and O-2. The introduction of helium gas remarkably enhances the spin-lattice relaxation rate, suggesting the p articipation of the collisional process of helium atoms in the spin re laxation from the dangling bond spins to the lattice. Taking into acco unt an exceptionally large condensation of helium gas, this proves tha t ACF has ultra micropores which can accommodate only the small diamet er helium atoms, resulting in a novel molecular sieve effect.