Internal conversion as second order process with electric dipole operator

Abstract

Classical consideration of internal conversion (IC) is one step process with the nonadiabatic coupled operator within the first order perturbation theory between the initial and final electronic states. We suggest considering the IC as the second order two step process with the electric dipole operator (d). Within this approximation the initial state is excited electronic state and the final one is the ground electronic state. The electronic excited energy in converted into the excitation of C-C bonds with the virtual photon emission at the first step. After that the virtual photon is absorbed by X-H (X = C, N and O) bonds. This mechanism can be important for the influence of external field on the IC process, too. It is called the induced effect. Estimation of two step process with d operator for two compounds: Azatrioxa[8]circulene (ATOC) and heptamethine cyanine (IR808) shows that this effect is noticeable when the external electric field is about 108 V/m - 109 V/m and the energy gap between the initial and final electronic states is about 10000–12000 cm−1.