Transfer rates for the coupled coherent and incoherent motion of excitons

Energy transfer rates for the coupled coherent and incoherent motion of excitons in molecular crystals are derived starting from the Haken-Strobl model. It is shown that the situation discussed recently by Kenkre and Knox on the basis of generalized master equations as well as the limits of fast (Perrin) and slow (Foerster) energy transfer are regained as limiting cases. (orig.)