Electron-vibrational interactions in polyatomic molecules

We review the literature on electron-vibrational interactions in polyatomic molecules. The analysis is based on an adiabatic theory that employs a single universal small parameter of the molecules, viz., the Born–Oppenheimer parameter. The principal results of the theory of electron-vibrational spectra are summarized. Special attention is paid to to the results that follow from a general analysis that is not based on concrete model. The theory is compared with experimental data for a wide range of chemical compounds (hydrocarbons with various structures, heterocyclic compounds, dyes). Possible mechanisms of broadening the electronvibrational line in liquid and solid solutions are discussed. Experimental data that demonstrate the role of various broadening mechanisms in concrete cases are cited. It is demonstrated by means of a number of examples (induced optical activity, dimers, excimers) that the adiabatic theory is significant in the analysis of the influence of intermolecular interactions on the spectral characteristics of the molecules. The theoretical analysis is illustrated with experimental data. The role of the adiabatic theory in the description of nonradiative transitions in polyatomic molecules is briefly considered. Particular attention is paid to a discussion of the role of chemical processes that accompany nonradiative transitions. Some additional problems faced by theory and experiment are indicated in the conclusion.