EFFECTS OF LIGHT DOPING ON THE VIBRATIONAL-MODES OF FINITE-LENGTH POLYACETYLENE CHAINS

With a local site-impurity potential in the framework of the Su, Schri effer, and Heeger (SSH) model, both the dopant dependence and the chai n-length dependence of the vibrational modes related to charged solito ns in a finite trans-polyacetylene chain have been studied. The numeri cal calculations showed that the well-known Goldstone mode will be pin ned by the dopant potentials as well as by the chain ends. Two localiz ed modes were found in the acoustic-frequency branch. The results are in agreement with the infrared-active vibrational modes also observed in lightly doped polyacetylene cases. A comparison with the photoexcit ation measurements has been given.