Perturbation inducing excitation-energy transfer between two molecules

The problem of the selection of the perturbation operator for a time-dependent perturbation description of excitation-energy transfer between two molecules is raised in this Letter. Then we attempt to determine the best representation of the perturbation through analysis of the nature of initial and final states in the process of the excitation-energy transfer. We concluded that not intermolecular interaction but nonadiabatic interaction must be regarded as the perturbation inducing the excitation-energy transfer.