Line broadenings within the alkali metal hyperfine multiplets of ion pairs and triple ions. A theoretical approach

Abstract

The effect of rotational diffusion on the metal hyperfine multiplets in the e.s.r. spectra of ion pairs and cationic ion triplets of alkali metal cations and aromatic radical anions is investigated theoretically. The triple ion of lithium and pyrazine is chosen as a model system; the broadening parameters are calculated for various structures of the triple ion. The results indicate that the anisotropic lithium hyperfine dipolar couplings, being modulated simultaneously with the anisotropic g-tensor, produce high-field broadening of the lithium septet, irrespective of the positions of the cations. Furthermore, it is concluded that there is no triple ion structure for which all the lithium broadening parameters vanish. Finally it is found that the calculated parameters are very small. In general, the anisotropy of the alkali hyperfine coupling in ion pairs and triple ions will be insufficient to account for the linewidth variations observed in these systems.