Handbook of Solvents - George Wypych - ChemTech - Ventech!

766 Roland Schmid
E r = E i + E s [13.1.25]
where:
Ei inner-sphere reorganization energy
Es solvent reorganization energy
For outer-sphere ET the solvent component Es of the reorganization energy
E s = e 2 c og [13.1.26]
is the product of the medium-dependent Pekar factor c o =1/ε ∞ -1/ε sand a reactant-dependent
(but solvent independent) geometrical factor
g = 1/2R a + 1/2R d -1/R [13.1.27]
where:
R the donor-acceptor separation
e the electron charge
Further advancements included calculations of the rate constant preexponent for
nonadiabatic ET, 132 an account of inner-sphere 133 and quantum intramolecular 134-136 vibrations
of reactants and quantum solvent modes. 137,138 The main results were the formulation
of the dependencies of the activation energy on the solvent dielectric properties and reactant
sizes, as well as the bell-shaped relationship between ΔF and ΔFo. The predicted activation
energy dependence on both the solvent dielectric properties 139,140 and the donor-acceptor
distance 141 has, at least qualitatively, been supported by experiment. A bell-shaped plot of
ΔF vs ΔFowas obtained for ET in exciplexes, 142 ion pairs, 143 intramolecular 144 and
outer-sphere 145 charge shift reactions. However, the symmetric dependence predicted by eq.
[13.1.24] has not yet been detected experimentally. Instead, always asymmetric plots of ΔF
against ΔFo are obtained or else, in the inverted region (ΔFo