Recombination of ion pairs created by photoexcitation of viologen complexes is studied by a theory accounting for diffusion along the reaction coordinate to the crossing points of the electronic terms. The kinetics of recombination convoluted with the instrument response function are shown to differ qualitatively from the simplest exponential decay in both the normal and inverted Marcus regions. The deviations of the exponentiality are minimal only in the case of activationless recombination and are reduced even more by taking into consideration a single quantum mode assisting the electron transfer. (C) 2008 Elsevier B.V. All rights reserved.