Viscosity Dependence of Iodine Recombination
Iodine photodissociation provided one of the original examples of the cage effect in liquids. Since then, the concept of a cage has become of central importance to chemists in guiding and understanding their choice of solvents for particular chemical reactions. Recently, HOFFMAN, et al.  applied picosecond techniques to study the dissociation and subsequent recombination of I in CCl4 and hexadecane. They showed that the recombination occurs in two time scales, a very short (around 100 nsec) and a much longer one (greater than l nsec.). This was interpreted as a direct demonstration of the cage effect. The short time decay is the recombination of caged radicals (geminate) and the long time decay is due to recombination of randomly diffusing I atoms (nongeminate). This experiment provides a good opportunity to test various diffusion theories, brownian motion theories, and molecular dynamics descriptions of translational motion in liquids. Thus, we have extended these experiments to study the recombination as a function of solvent viscosity and structure.
KeywordsProbe Transmission Solvent Viscosity Viscosity Dependence Cage Effect Cage Radical
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