Picosecond Dynamics of Organic Ionic Intermediates

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9408354 Peters U. of Colorado The dynamics of photodissociation of alkyl and vinyl halides will be examined by picosecond absorption spectroscopy. The reaction mechanism involves both homolysis and heterolysis to produce radical pairs and contact ion pairs in polar solvents. On the picosecond time-scale the contact ion pairs decay by covalent bond formation as well as diffusional separation to form solvent separated ion pairs. The latter species decay by collapse to a contact ion pair or diffusionally separate to free ions. The project will include: (1) An investigation of the mechanism for the photochemical production of radical pairs and contact ion pairs, (2) The determination of activation parameters for covalent bond formation between a carbocation and an anion, and how solvent effects this process, (3) The role of solvent on the inter conversion between contact and solvent separated ion pairs, and how this depends on molecular structure of the ions. This grant by the Organic Dynamics Program supports the continuing work of Professor Kevin S. Peters at the University of Colorado. A pulsed ultraviolet laser beam in the picosecond (one billionth of a second) domain will be used to break carbon-chloride bonds with the goal of generating positively charged carbon species (carbocations). These reactive intermediates may be in direct contact with a negatively charged species (an anion) or the carbocation and anion may be separated by a limited number of solvent molecules. The dynamic behavior these contact and solvent separated ion pairs as a function of solvent and molecular structure will be investigated.