Electrochemical Activation Parameters for Surface-Attached Reactants Evaluation of Unimolecular Frequency Factors for Representative Ligand-Bridged Reactions.
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The temperature dependence of unimolecular rate constants are reported for the one-electron reduction of various CoIII and CrIII reactants attached to mercury or silver surfaces via either thiocyanate or various thiophenecarboxylate ligands. Combining the ideal activation enthalpies obtained at a constant electrode potential using a nonisothermal cell arrangement with the corresponding activation entropies estimated from reaction entropy data enables values of the unimolecular frequency factor, A sub et, for the elementary electron-transfer step to be evaluated. Values of A sub et close to 10 to the 13th powersec-01 were obtained in this manner for the thiocyanate-bridged reactions at mercury, indicating that the electronic transmission coefficient approaches unity, i.e., the reactions are adiabatic.
- Physical Chemistry