Interplay between solvent effects of different nature in interfacial bond breaking electron transfer.

Solvent dynamics effects on electroreduction of peroxodisulphate anion on mercury electrode (a typical bond breaking electron transfer reaction) are explored in the framework of the Sumi-Marcus model. The reaction three-dimensional free energy surface is constructed using the Anderson model Hamiltonian. A new interpretation of short- and long-time survival times is presented as well. Since the reduction is assumed to proceed from aqueous sucrose and glucose solutions of different concentrations (which are used to vary the solution viscosity), unavoidable changes in the Pekar factor (static effect) are also taken into account. The results of model calculations are employed to interpret challenging experimental data on nonmonotonous constant rate vs solution viscosity dependence reported earlier (in part, appearance of an ascent plot). The influence of mixed solvent composition on the reaction rate and transfer coefficient is explained in terms of the saddle point avoidance in the vicinity of activationless discharge. Splitting of the reaction coordinates into slow (solvent) and fast (intramolecular) ones is argued to be crucial, as the most important reaction features cannot be described by means of more simplified models, even if both static and dynamic effects are addressed.