RECOMBINATION KINETICS OF TRIPLET RADICAL ION-PAIRS ADSORBED ONTO MICROCRYSTALLINE CELLULOSE STUDIED BY DIFFUSE-REFLECTANCE LASER FLASH-PHOTOLYSIS

Recombination kinetics of radical ion pairs formed by electron transfe r from triphenylamine to triplet benzophenone, 9,10-anthraquinone, dur oquinone, and 2,6-diphenyl-1,4-benzoquinone coadsorbed onto porous mic rocrystalline cellulose has been studied by using the diffuse-reflecta nce laser flash photolysis technique. The kinetics is nonexponential e xtending over at least 4 orders of magnitude in time scale from almost -equal-to 0.1 mus up to 1 ms. The initial part of the kinetic curves ( about 75% of conversion from the initial maximum absorption) can be de scribed by a Gaussian distribution of the logarithm of the rate consta nt at various adsorption sites, while the final part of the decay curv es follows the diffusion-like behavior-concentration vs t-1/2. Applica tion of an external magnetic field as well as oxygen has no observable effect on the radical ion pair decay. The roles of predominant static reaction pathways as well as those of dynamic reaction ones are discu ssed.