Narrowing mechanisms of ESR line of (CH)X

Abstract

Abstract Electron Spin Resonance (ESR) on the paramagnetic centers in undoped polyacetylene (CH)X was studied and the effects of the thermal isomerization and the oxidation on the narrowing mechanisms of an ESR line were discussed. The ESR linewidth at 4.2K is found to be proportional to n−1/3 (n: spin density in (CH)X) which means that the static narrowing mechanism was three-dimensional exchange narrowing. The linewidth at room temperature changed with the thermal isomerization and oxidation of (CH)X and was explained by two opposed mechanisms; motion of spins in the conjugated chain and restriction of the motion by cutting off the conjugated chain by cis content or oxidation. The temperature dependence, the thermal isomerization dependence and the oxidation dependence of the ESR linewidth of the undoped polyacetylene can be explained by the three- dimensional exchange narrowing and the motional narrowing mechanisms. Only one kind of spins (neutral solitons) in the conjugated chain is considered to cont...