An electron spin resonance study of pure anthracene doped with alkali metals

When pure anthracene is melted under a pure nitrogen atmosphere in the presence of an alkali metal, the metal dissolves forming a blue-green melt which exhibits an electron spin resonance (e.s.r.) signal. The polycrystalline samples of the solid system (MAn) obtained by cooling the melt also exhibit e.s.r, signals but with a line-width greater than that seen in the melt. The Lorentzian line-shapes in the solid and the melt indicate that the electrons producing the signals are either delocalized, or clustered and undergoing exchange interaction. The following features are discussed: the lack of hyperfine structure in the melt except for a special case; the Curie dependence of the susceptibility; the dependence of the g-values on the alkali metal; the shifts of the g-values on melting the samples; the behaviour of the line-width with respect to deuteration of anthraoene and with respect to the different alkali metals; and the dependence of the spin-lattice relaxation time on the alkali metal and on whether the sample was solid or molten. The features indicate that the electrons behave as simple doublets, are clustered with the alkali-metal complex in the solid and undergo exchange interaction, produce motional narrowing of lines in the melt, and produce a line-width mainly dependent on the alkali metal ions in the solid and to a lesser extent in the melt.