Vibronic coupling in excited electronic states of complex molecules

Different aspects of the theoretical interpretation and utilization of the fine-structure vibronic spectra of polyatomic organic molecules in solution for determining characteristics of the electronic excited states of such molecules, such as the orbital type, localization of excitation on fragments, change of nuclear configuration, etc., are presented. The adiabatic approximation with Frank–Condon and Herzberg–Teller coupling is studied. A great deal of attention is devoted to the phenomenon of suppression of most spectral lines in the range corresponding to allowed transitions in vibronic spectra. Some reasons for this phenomenon are discussed.