Raman Scattering by Optical Phonons In TaSe3 and NbSe3

Abstract Room-temperature Raman spectra have been obtained between 20 cm−1 and 400 cm−1 on the low-dimensional metals TaSe3, and NbSe3. The Ag spectra exhibit numerous closely spaced lines corresponding to vibrational modes with displacement vectors perpendicular to the chain axis. To interpret these spectra we have made direct use of the bond-strength results of our lattice dynamical model for ZrSe3, which has a similar prismatic chain structure. The broad correlations obtained between the data and the calculated frequencies indicate that the C2V symmetry of the chain is preserved in the Bg vibrations; that strong metal-selenium bonds exist which link the chains into layers; and that Se-Se pairing within the chains is weaker and more varied in TaSe3 and NbSe3 than in ZrSe3.