Isotope effect on formation energy of soliton in t-polyacetylene

The formation energy of a soliton was derived in the TLM model to be 2Δo/π which is independent of the mass of the polymer atoms. The electron-phonon coupling is shown to induce anharmonic lattice vibration. They give a contribution to the formation energy. The amplitude mode formalism is used. Among dynamical degrees of freedom in the lattice vibrations, a translational mode of the soliton is separately examined, since it corresponds to a Goldstone mode. We get a difference in the formation energy between the two istopes (CH)x and (CD)x of about 0.03eV. The soliton trapping aroung the defects or impurities can enlarge the isotopic difference.