CS₂ TCNQ₃ Revisited: A Detailed Description of its Ground State Through a Reinterpretation of the Optical Spectra

Abstract

A substantially complete and definite interpretation of Cs₂ TCNQ₃ infrared and Raman spectra (in the region of intramolecular modes) is achieved. The presence of vibronic absorptions in the infrared spectra is quantitatively accounted for in terms of a newly introduced model of electron-molecular vibration (e-mv) interaction, which takes into consideration the coupling with both the intra- and inter-trimer charge transfer transitions. The same model, with the same parameters, is also able to explain the so far unrecognized e-mv perturbation (frequency shift) of the Raman active totally symmetric modes. The re-examination of the Cs₂ TCNQ₃ optical spectra thus shows that the electronic charge on the Cs₂ TCNQ₃ molecular sites differs appreciably from zero and one, being 0.1₄ and 0.9₃ for centric and non-centric TCNQ molecules, respectively.