Marcus theory confirmed experimentally

In experimental studies of photoinduced electron transfer reactions, the free energy dependence of the quenching of a particular metal complex (e.g, Ru(bpy)3 + ) by a series of structurally related quenchers of known properties is used to confirm the calculated potential of the excited state couple and to estimate its exchange rate. For a given quencher a graded series of polypyridine complexes with different substituted bpy/phen ligands can also be used equivalently. These provide a set of experimentally measured data to check the observation of normal and inverted behaviour predicted by Marcus theory under certain conditions. Rate constants for back electron transfer of photoredox products have been measured in a similar manner in some cases and these were also subjected to analysis. 

One particular example of the use of pulse radiolysis to general chemistry was the work of Miller and co-workers on the rates of electron-transfer reactions. These studies, which were begun using reactants captured in glasses, were able to show the distance dependence of the reaction of the electron with electron acceptors. Further work, where molecular frameworks were able to fix the distance between electron donors and acceptors, showed the dependence of electron-transfer rate on the energetics of the reaction. These studies were the first experimental confirmation of the electron transfer theory of Marcus. 

For outer sphere electron transfer reactions the Butler-Volmer law rests on solid experimental and theoretical evidence. An outer sphere electron transfer reaction is the simplest possible case of an electron transfer reaction, a reaction where only an electron is exchanged, no bonds are broken, the reactants are not specifically adsorbed, and catalysts play no role (see, e.g.. Ref. 2). Experimental investigations such as those by Curtiss et al. [206] have shown that the transfer coefficient of simple electron transfer reactions is independent of temperature. The theoretical basis is given by the theories of Marcus [207] and of Levich and Dogonadze [208] these theories also predict deviations at high overpotentials which were experimentally confirmed [209, 210]. 

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