Isotope effect on formation energy of solitonin t-polyacetylene

Summary form only given. The formation energy of a solion. was derived in the TLM model to be 2/spl Delta//spl ogr/(//spl pi/ which is independent of the masses of the polymer atoms. Several years ago, preliminary measurements of the excitation profiles for the photogeneration of solitons in t -(CH)/sub x/ an in t -(CD)/sub x/ suggested an isotope effect of the magnitude of 0.03eV (1]. It was too large to be accounted for by the difference in the zero-point energy of lattice vibrations around the soliton determined in Ref.[2]. We estimate effects of the electron-phonon coupling, particularly, through modifications of electronic energy levels. A model by the amplitude mode formalism is used and the coupling is taken into account up to the second order. Among dynamical degrees of freedom in the lattice vibration, 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 isotopes of about 0.01eV.