The equations of motion of the cou led electron-phonon system are integrated in real time for the model of yacetylene recently proposed. To illustrate the physical behavior of this nonlinear system we consider the time evolution starting from three physically relevant configurations: (i) end generated soliton, (ii) electron-hole pair generation of a charged soliton-antisoliton pair, and (iii) the dressing of an injected electron. The calculations show that the system relaxes within a time of order 10-13 sec, converting excited electron-hole pairs into soliton-antisoliton pairs.Polyacetylene (CH). is a simple linear polymer formed as a chain of CH groups. The trans configuration, corresponding to a herringbone structure of CH groups, is the stable phase at room temperature and below. Because undoped (CH)X has exactly one r electron per CH group, the traditional view is that the ground state exhibits a lattice distortion or dimerization in which bond lengths between CH groups are alternately longer and shorter than the average bond length a (Fig. 1). In the language of condensed matter physics, trans (CH)X has undergone a commensurate Peierls distortion of index 2. The doubling of the size of the unit cell introduces a periodic potential acting on the ir electrons which opens a gap 2A in the -r energy band structure at the Fermi surface, converting the one-dimensional metal into a semiconductor (1), as is observed.However, evidence is growing (2-4) that, instead of the familiar electron and hole excitations characteristic of a conventional semiconductor, the stable low-energy charge-carrying excitations in (CH), are charged solitons, S. These excitations are in essence charged domain walls (2, 3, 5) separating regions with different ground state order as illustrated in Fig. 1. The A and B ground states are related by interchanging double and single (short and long) bonds. As Su et al. (2, 3) have shown, S+ and S-have zero spin in contrast with holes and electrons which have spin 1/2. Also, the neutral soliton SO has spin '/2. The width of the soliton is approximately 14 lattice spacings for (CH)X and its mass is remarkably small, roughly six electron masses. There is considerable experimental evidence supporting these results.In order to gain further insight into dynamical processes in (CH)X, such as electrical conductivity, spin diffusion, optical absorption, photoconductivity, etc., we have carried out a real-time integration of the equations of motion describing the coupled electron and phonon fields. Following Su et al. (2,3,
