CHARGE SEPARATION RECOMBINATION REACTIONS IN NONPOLAR FLUIDS - A MOLECULAR DESCRIPTION

The activation energy for intramolecular electron transfer in non-pola r fluids is derived in analytical form by expressing it through the ch emical potential of solvation of a dipole of complex dipole moment ($) over tilde mu. The reorganization energy of the non-polar liquid mani fests itself as a nonlinear liquid response beginning with terms propo rtional to ($) over tilde mu(4) upwards in the expansion of the chemic al potential over the solute dipole moment. The reorganization energy is represented as the sum of two terms arising from liquid polarizatio n and density reorganization, with the latter component being of much greater importance. It is suggested that electron transfer in non-pola r solvents is promoted by fluctuations of the number of molecules in t he first coordination sphere of the donor-acceptor complex. Since the molecular polarizability is temperature independent, the reorganizatio n energy is inversely proportional to temperature. This fact can lead to a maximum in the temperature dependence of electron transfer rates, and hence to negative activation enthalpies. Comparisons of theoretic al predictions are made with experimental thermochromic shifts of char ge recombination optical bands.