Cation migration between two unequivalent sites in 4-cyano pyridine alkali metal ion pairs

The ESR spectra of 4-cyanopyridine alkali metal ion pairs were recorded at different temperatures. The different hyperfine components are selectively broadened by a dynamic process which affects the linewidths. The analysis of the linewidth parameters has been accomplished as due to a jumping process of the cation between two unequivalent positions. An ab initio calculation of the potential energy surface of the radical anion shows that the motion should take place between two positions near the two nitrogen atoms in the molecular plane. Modulation of the anisotropic interactions by the tumbling motion of the ion pair cannot explain the observed data.