Infrared studies of the phase transition in the organic charge transfer salt (ET)2C(CN)3

Polarized reflectance spectra from single crystals and powder absorption spectra of (ET)2C(CN)3 salt are measured in the middle IR region. The metal-insulator phase transition influences the IR spectra especially within the range of C  C vibrations. The strong coupling of electrons with v27(b1u) mode (antisymmetric stretching of C  C ring bonds) is observed.