The 1320-nm excited FT-Raman spectra of Na-doped trans-polyacetylene

The FT-Raman spectra of trans-polyacetylene doped with Na at various concentrations were observed with the 1320-nm laser line. Doping-induced Raman bands for lightly doped trans-polyacetylene were observed for the first time. The observed wavenumbers of the ν1 and ν4 bands (C=C and C=C stretches) of lightly doped trans-polyacetylene are lower than those of the corresponding bands of pristine trans-polyacetylene, whereas the contrary is the case for heavily doped trans-polyacetylene. The origins of doping-induced Raman bands are discussed in terms of solitons and polarons.