Enhanced Excitation Transfer during Vibrational Relaxation after Pumping and Generalized Förster's Formula

Electron or excitation transfer can be enhanced during vibrational relaxation after optical excitation of a donor. When it occurs after vibrational relaxation with a thermal activation energy $E_A$, enhanced transfer during vibrational relaxation is also governed by an activation energy $E_H$ which, however, is smaller than $E_A$ or even vanishes. The decrement $E_A-E_H$ depends on the total energy of vibrations triggered by optical excitation, and also on their average direction relative to that of the activation barrier for transfer in the phonon-coordinate space.