| Abstract
| - The ultrafast reaction dynamics following 295-nm photodissociation of Re2(CO)10 were studiedexperimentally with 300-fs time resolution in the reactive, strongly coordinating CCl4 solution and in theinert, weakly coordinating hexane solution. Density-functional theoretical (DFT) and ab initio calculationswere used to further characterize the transient intermediates seen in the experiments. It was found that thequantum yield of the Re−Re bond dissociation is governed by geminate recombination on two time scales inCCl4, ∼50 and ∼500 ps. The recombination dynamics are discussed in terms of solvent caging in which thegeminate Re(CO)5 pair has a low probability to escape the first solvent shell in the first few picoseconds afterfemtosecond photolysis. The other photofragmentation channel resulted in the equatorially solvated dirheniumnonacarbonyl eq-Re2(CO)9(solvent). Theoretical calculations indicated that a structural reorganization energycost on the order of 6−7 kcal/mol might be required for the unsolvated nonacarbonyl to coordinate to a solventmolecule. These results suggest that for Re(CO)5 the solvent can be treated as a viscous continuum, whereasfor the Re2(CO)9 the solvent is best described in molecular terms.
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