RESONANT RAMAN-SCATTERING FROM A CHARGE-DENSITY-WAVE SYSTEM (TTF-TCNQ)

We report the observation of strong new lines in the resonant Raman sc attering from a powder sample of TTF-TCNQ, as the temperature is lower ed and the fluctuating charge-density-wave (CDW) occurs. The intensity of these lines increases with decreasing temperature. The new lines a re assigned to normally infrared-active B-3u out-of-plane intramolecul ar distortion modes of TCNQ, in agreement with the results of an X-ray study which found that the CDW on the TCNQ chain involved such an out -of-plane distortion of the TCNQ molecule. The new lines are much weak er in TSeF-TCNQ. (C) 1998 Elsevier Science Ltd.