The influence of interatomic forces on the spectra of polyacetylene has been analyzed in detail by means of molecular dynamics simulations. Several simulations have been undertaken in which different terms have been added to the force field. Stretching, bending, torsional, and nonbonded forces have been subsequently incorporated in the simulations, in order to point out the specific spectral effects of every interaction. It has been obtained that the influence of all interatomic forces is qualitatively the same in both the trans and cis systems except for the torsions involving hydrogen atoms, which are relevant for the spectra parallel to the chain axis in the cis system, but not in the trans. Stretching and bending forces have a strong influence on the spectra parallel to the chain axis. The interchain forces do not significantly affect any of the spectra. Moreover, the results obtained in our simulations have been used to assign the experimental frequencies of polyacetylene to particular microscopic interactions. (C) 2003 American Institute of Physics.