Vibrational spectra of β″-(ET)3X2 (X=HSO4, ClO4) salts

Abstract The IR and Raman spectra of β″-(ET)3X2 [X = HSO4 and ClO4] salts were measured at various temperatures below 300 K. The ν2 and ν27 modes exhibit the splitting into two peaks below the metal–insulator transition temperature. This phenomenon is ascribed to the charge ordered (CO) state. The CO patterns of the presented compounds were determined on the basis of the numerical calculation of the vibronic ν3L mode. The assignment of the ν27 mode of ET+ was confirmed through the measurement of the reflectance spectra of the 1:1 salts (ET)ClO4, (ET)AuCl2Br2 and the isotope analogues. The ν27 mode is the efficient probe to the site charges of the ET salts.