抄録
The polarized reflection spectrum indicates that the organic metal (BEDT-ATD)2PF6(THF) has a quasi-one-dimensional band structure with a narrow bandwidth of ca. 0.24, eV. The intra-HOMO-band transition of (BEDT-ATD)2PF6(THF) shows two broad peaks at ca. 1000, cm-1 and 1700, cm-1 which feature is quite different from the Drude-like metallic absorption. The vibronic bands interfering with this absorption band begin to grow as dips at 100, K, which means that the screw-axis symmetry of the space group P21/a is broken below 100, K. This broken symmetry is supported by the splitting of the Raman band of a charge-sensitive vibrational mode. It is suggested from the comparison with the thermopower's data that this structural change has no long-range-ordered modulation above 50, K. The intensity of some infrared-active vibrational modes is enhanced by the intra-molecular charge oscillation whose optical transition appears at 4600, cm-1.
