Lattice dynamics of polyacetylene as a one-dimensional system: Part II. Doping-induced disorder

The quadratic valence force field derived in Part I of this study for perfect trans-polyacetylene is used and adapted for the study of the doping-induced IR absorption of polyacetylene. The lattice dynamics of a one-dimensional disordered system is treated with the introduction of structural defects to represent the doping sites. Concentration, distribution, size of the defects and inhomogeneity of the doping are all considered. Two models for the defects are analyzed; one representing the “soliton” and the other, equally acceptable on chemical grounds, representing centro-symmetric defects. It is concluded that the IR spectrum observed for doped polyacetylene does not provide unequivocal evidence for the existence of solitons. Alternative explanations are equally acceptable from the spectroscopic viewpoint. The structural information derived from lattice dynamics and spectra is discussed in detail.