Resonance Raman Scattering from Neutral and Doped Polyacetylene

Abstract

Abstract A complete assignment for the modes obtained from resonance Raman scattering on cis‐ and trans‐polyacetylene is reported. The Raman lines in the cis‐isomer indicate a well expressed one dimensional behaviour of the chain. From the line profile and line position of the resonance enhanced CC stretch modes in the trans‐isomer a chain length distribution of modified Gaussian form with a maximum at 30 CC double bonds and a half width of 20 CC bonds is deduced. The experimental results confirm the alternating bond model and lead to a sine wave chain potential with amplitude 1.9 eV. The effective mass of the π‐electrons is determined for the first time experimentally to be equal to the free electron mass. Intercalating the cis‐polymer with AsF 5 results in a cis‐trans‐transition and a pronounced chain shortening. It is concluded from the experiments that the intercalating molecules precipitate between the chains.