Subterahertz electrodynamics of [ salts

The terahertz-subterahertz spectra of the complex permittivity and dynamic conductivity of polycrystalline [(TMTSF).sub.2]Cl[O.sub.4] and [(TMTSF).sub.2]P[F.sub.6] samples are measured quantitatively. The spectra of [(TMTSF).sub.2]Cl[O.sub.4] have absorption lines at frequencies of 7 and 30 [cm.sup.-1]. The obtained temperature dependences of the line parameters in the range 5-300 K cast some doubt on the earlier concept of their phonon origin. An excitation is detected at temperatures below 20 K in the frequency range near 30 [cm.sup.-1], and its nature is related to the activation of a transverse acoustic phonon caused by the folding of the Brillouin zone due to the ordering of noncentrosymmetrical anions below 20 K. An increase in the carrier relaxation rate is found in this temperature range, which indicates a close relation between the electron and phonon subsystems in [(TMTSF).sub.2]Cl[O.sub.4]. Sings of additional low-energy excitations that should manifest themselves at frequencies below 1-2 [cm.sup.-1] are detected. [(TMTSF).sub.2]P[F.sub.6] containing centrosymmetrical anions has no absorption lines in the frequency range 3-20 [cm.sup.-1] and the temperature range 5-300 K.