Geminate Recombination Kinetics of Triplet Radical Pairs in Glycerol: Magnetic Field Effect

Article abstract of DOI:10.1021/j100338a045

Laser flash technique has been used to record the geminate recombination kinetics of triplet radical pairs (RP) generated from benzophenone photoreduced with p-cresol in the viscous glycerol/p-cresol binary solvent.The RP decay kinetics fits fairly into the first-order law.At the same time the kinetics curve features a manifest slow descending "tail" that follows the φ_infinite-φ(t) ca. t^-1/2 relationship, where φ_infinite is the (total) cage effect and φ(t) is the time-dependent cage effect.The geminate recombination kinetics is closely described in the entire time range (0 10 μs) by the function originating from Noyes' treatment of molecular dynamics, φ(t) = φ_infinite erfc (k_Nt^-1/2) where k_N is a constant.An increse of solvent viscosity (decrease of temperature) causes an increase of φ_infinite and deceleration of RP dissociation.The geminate recombination kinetics is described by mutual diffusion coefficients smaller than the sum of the diffusion coefficients of individual radicals.The probable reason of such behavior is that there is a strong correlation between the molecular motions of radicals positioned within several molecular diameters from each other.Application of an external magnetic field (H infinite by 10-50percent.The extent of the magnetic effect heavily depends on H when H<*>0.1 T and is practically independent of H when 0.1<*>H 0.1 T, the magnetic field acts by the hfc mechanism and by slowing the paramagnetic relaxation due to the hfc anisotropy and dipole-dipole coupling between unpaired electrons.