RAMAN SCATTERING OF ORGANIC CHARGE-TRANSFER SALTS CONTAINING BEDT-TTF CATION

Raman scattering of several organic charge-transfer salts containing BEDT-TTF of ET cation such as \kappa-ET₂Cu(NCS)₂, \beta_L-ET₂I₃, \alpha-ET₃Cl₂. 2H₂O, \alpha-ET₃ (ReO₄)₂ and ETFeBr4 were measured and the variations of the frequencies of C=C bonds of ET molecules on charge transfer were observed. It is found that the energy of C=C stretch modes shows a general downward shift upon ionisation of ET molecule. In addition, we have observed the Raman spectra of C=C stretch vibratinns in \kappa-ET₂Cu(NCS)₂ single crystal on going through T_c(～10.4 K) and found no detectable effect during the superconducting phase transition.