Electron-molecular vibration coupling in organic charge-transfer salts: application of spectroscopic and Hubbard models

Spectroscopic and Hubbard models were utilized for analysis of vibrational spectra of organic monovalent charge-transfer (CT) salts with dimerized structures. Within the framework of a dimer approach we showed origin of intense infrared active electron-vibrational (vibronic) bands and obtained an expression for their frequency shifts relatively to matching Raman active totally symmetric vibrations. The theory predicts an important relationship between intensities and frequencies of the vibronic bands and is in good agreement with experimental data for BEDT-TTF-based and TTF-based CT complexes. Existence of the universal relationship between the two easy measurable quantities allows to make a simple evaluation of coupling constants for the substances directly from the experimental spectra.