Coupling Between Charge Transfer and Intramolecular Vibrational Modes in (TMTSF)₂X, X = PF₆ or ReO₄

Abstract

The Bechgaard’s salts ¹, of general formula (TMTSF)₂X represent one of the most interesting family of quasi 1-d organic conductors. They have been extensively studied during the past decade by a variety of techniques ^2,3,4,5. Nevertheless, among the various light scattering experiments ^6,7,8,9 performed, only Resonant Raman Scattering (R.R.S.) enabled some of us ^8,9 to record more than a few modes. This was first reported⁸ for X = PF₆ which remains metallic down to OK. Only some of these modes, namely those which are the totally symmetric modes of the isolated TMTSF molecule, were then identified. More recent experiments⁹ on X = PF₆, and also on X = ReO₄ which undergoes a metal insulator transition at 182 K have enabled us to interpret some of the extra modes as resulting from a dynamical charge transfer (C.T.) mechanism, a phenomenon typical of these organic conductors.