Optical properties of organic conductor (ET)4Hg3I8 : alternative type of electron-vibrational interaction

The reflectivity spectra of single cry~tal~ of (ET )iHg,Ix and jd~-ET)iHgilx were studied. In contrast with earlier studied clorineand brominemercur~lte compounds of the series (ET jjHg, ~-Xz IX Cl, Br, I), the spectra of iodinemercurate compounds exhibit low reflectivity without well-defined plasma edge and without electron-vibrational bonds in the region 1000400 cm '. The latter fact may be due to electron-vibrational interaction with non-totally symmetric modes which m~ly originale from peculiaritie; of crystal uructure of iodinemercurate compound,. A phase transition of the fir;t type i~ observed bath for (ET)iHg,Ix and (d~-ET)jHgilz. At the transition temperature a jump in conductivity and reflectivity i~ ob;erved.