Peculiarties of the Electronic and Electron Vibrational Spectra of Organic Conductors: BEDT-TTF Salts of Alpha-Type Structure

摘要

Polarised infrared reflectivity spectra of some ET-based conducting salts of alpha-type structure are measured and compared: (ET)_2I_3 (Ⅰ), (ET)_2TIHg(XCN)_4 (X ο S,Se) (Ⅱ) and (ET)_8[Hg_4Br_(12)(CH_3C_6H_4Cl)_2] (Ⅲ). For both Ⅰ and Ⅱ the electronic reflectivity is greater for the polarisation perpendicular to ET stacks. However, a resolved electron vibrational band in the region of 1 100-1 400 cm~(-1) is observed for Ⅱ in the polarisation characterised by lower electronic reflectivity in contrast with the spectra of Ⅰ. Another difference between Ⅰ and Ⅱ is the absence of the pronounced plasma edge in the region of 4 000 cm~(-1) in the spectra of Ⅱ, which may be due to high electron damping. For Ⅲ the electronic reflectivity is low and no resolved electron vibrational band in the region of 1 100-1 400 cm~(-1) is observed. The peculiarities of the electron-vibrational spectra of Ⅰ, Ⅱ and Ⅲ may be due to the details of the crystal structure.