U. Werner et H. Staerk, MAGNETIC-FIELD EFFECT IN THE RECOMBINATION REACTION OF RADICAL-ION PAIRS - DEPENDENCE ON SOLVENT DIELECTRIC-CONSTANT, Journal of physical chemistry, 99(1), 1995, pp. 248-254
The influence of external magnetic fields on the reaction yield of rec
ombining radical ion pairs of polymethylene-linked acceptor/donor syst
ems (pyrene/N,N-dimethylaniline) is investigated in solvents of varyin
g dielectric constant (epsilon = 7-37). Different bulk DKs are also ad
justed with binary solvent mixtures. Similar to nonlinked radical ion
pairs of the same type, the highest magnetic field effects (MFEs) on t
he yields of products measured (exciplexes and pyrenyl triplets) are f
ound in solvents of medium DK (epsilon approximate to 20). In such lin
ked systems, only geminate recombination is necessarily possible, whil
e homogeneous recombination does not occur. We conclude, therefore, th
at earlier theoretical models for the explanation of the so-called ''m
edium-DK MFE maximum'' in free-radical ion pair systems must be consid
ered obsolete, These earlier models are mainly based on the competitio
n between geminate and homogeneous recombination pathways. Based upon
support from all present experimental results, an alternative model is
proposed which correlates the radical ion pair lifetime with the achi
evable magnitude of the MFE.