Up to the present, most models proposed to explain the outer-sphere electron-transfer reaction rates in solution imply a drastic reduction of the degrees of freedom of the solvent system. In this work we have tested the influence of these simplifications on the self-exchange reaction Fe+ + Fe2+ ⇄ Fe2+ + Fe+ in water. Several simulations of water clusters around each ion have been done by using the Monte Carlo method. Different constraints to the movement of water molecules have been imposed. It has been found that the probability of solvent fluctuations suitable for electron transfer to be produced tends to decrease as far as the number of degrees of freedom allowed to vary is increased. If all degrees of freedom are taken into account, these fluctuations have a very low probability and it is practically impossible to generate them upon starting from an equilibrium distribution of the solvent around the reactants. We have used an alternative strategy to get solvent configurations that favor the electron transfer. An explanation to justify these results is proposed. © 1989 American Chemical Society.
|Journal||Journal of Physical Chemistry|
|Publication status||Published - 1 Jan 1989|