DELOCALIZATION CONTRIBUTIONS TO POLYACETYLENE FORCE-FIELDS

The force fields of trans and cis-polyacetylene(PA) are obtained in in ternal coordinates by combining linear-response analysis of the Raman and ir shifts due to pi-electrons, molecular force-field methods, and the Huckel susceptibility of k not equal O phonons. We find transferab le electron-phonon coupling constants, exponential transfer integrals t(R), and coupling to CCC bends through the Coulomb potential V(R). Th e electronic response of cis-PA is 56% of the trans susceptibility, in dicative of reduced delocalization and an energy gap in the A(g) manif old due to third-neighbor V(R) terms.