EFFECT OF DEUTERATION ON THE ELECTRONIC AND ELECTRON-VIBRATIONAL PROPERTIES OF THE ORGANIC CONDUCTOR K-(D-8-BEDT-TTF)(2)[HG(SCN)(2)BR]

We present here for the first time polarized reflection spectra and op tical conductivity spectra of single crystals of the newly deuterated organic conductor k-( D-8-BEDT-TTF)(2) [Hg(SCN)(2) Br] at room tempera ture. The spectral region investigated is 700-40 000 cm(-1). We examin ed the effect of deuteration on electronic and electron-vibrational tr ansitions observed in the spectra. The observed shift of the electron ''dimer'' transition in the infrared toward lower frequencies upon deu teration is linked with an increase in the interaction between neighbo ring, mutually perpendicular dimers in the structure of the deuterated crystal. A lowering of the symmetry of the BEDT-TTF molecule is demon strated in crystals similar to k-(BEDT-TTF)(2) [Hg(SCN)(2)Br], relativ e to the symmetry D-2h of the free molecule. We refine the assignment of the spectral features determined by the interaction of electrons wi th the fully-symmetric intramolecular vibrations of the C=C, C-S, and C- C-H bonds of the BEDT-TTF molecule. (C) 1998 American Institute of Physics. [S1063-7834(98)00509-7].