VIBRATIONAL ASSIGNMENTS IN THE CONDUCTIVITY SPECTRA OF SEMICONDUCTING (TMTSF)2REO4 AND (TMTSF)2BF4 (WHERE TMTSF IS TETRAMETHYLTETRASELENAFULVALENE) FOR RADIATION POLARIZED PERPENDICULAR TO THE CHAINS

We present a vibrational analysis of the transverse E parallel-to b' conductivity of semiconducting (TMTSF)2ReO4 and (TMTSF)2BF4 (where TMTSF is tetramethyltetraselenafulvalene). We also report the results of a normal-coordinate calculation of the vibrations of the deuterated (TMTSF)+ molecule, which was used to assist in the reported assignments. The data were supplemented with powder spectra, which showed predominantly the infrared-active b1u modes. The E parallel-to b' spectra displayed the expected infrared-active b2u modes, as well as several totally symmetric a(g) modes resulting from the general site symmetry of the molecule. Unusual strength is noticed in the two b2u modes which are almost degenerate with the very intense nu-4(a(g)) doublet observed in the E parallel-to a spectra. In that polarization the strength is derived from electron-phonon coupling. There is, however, no such coupling observed in the E parallel-to b' polarization.