ANOMALOUS SPIN-LATTICE RELAXATION INDUCED BY HELIUM GAS IN MICROPOROUS CARBON

Microporous activated carbon fibers with huge specific surface area (3000 m(2)/g) have dangling bond spins at the peripheries of micro-graphitic domains. Spin-lattice relaxation of the dangling bond spins was studied by ESR measurements in the presence of various gases, He, Ne, Ar, H-2, N-2, O-2 The introduction of helium gas strongly enhances the spin-lattice relaxation rate 1/T-1, suggesting the contribution of the collisional process to the spin-lattice relaxation mechanism. The introduction of a simple model on the basis of the electric dipole-dipole interaction makes the calculation of 1/T-1 possible and the obtained result can explain the experimentally observed result.