Infrared Absorption and Reflection Spectra of Crystalline TCNQ Salts

Abstract

The polarised absorption and reflectance spectra of the three TCNQ salts pyridinium (TCNQh, triethylammonium (TCNQh and thermally damaged quinolinium (TCNQh indicate that the absorption features are governed by reflection characteristics. The maximum reflectance curve shows a broad minimum which corresponds to a negative dip in the real part of the dielectric constant and a broad maximum in the imaginary part, as calculated using a Kramers-Kronig analysis. This is ascribed to mobility gaps ariSing from a frequency·dependent lifetime within the valence band because of the scattering of electrons by 2kF phonons. The exact absorption spectra with all the phonon bands are also analysed and the correlations among the electron-intra·molecular vibration coupling, mobility gaps and the electronic states of charge density waves are discussed.