Ion Pairs in Liquids

In a homogeneous medium, radical ion pairs are formed by separation of opposite charges and, correspondingly, of spins of a neutral molecule. The charges are separated for different reasons, by chemical oxidation, ionizing irradiation, etc. The resulting radical ion pairs may have different distances between the opposite partners. If the distance is small, i.e. a few angstroms there is a strong electronic and magnetic interaction between the partners. This can lead to a substantial difference between the properties of ion pairs and isolated radical ions. In non-polar media these correlated pairs recombine very rapidly. In polar media they may be stabilized and exist for a long time due to solvation effects which weaken the Coulomb interaction. A large body of publications is devoted to the properties of such pairs (see, e.g. monograph [1].