Soliton pair generation in polyacetylene: A lattice relaxation approach

The theory of lattice relaxation and multiphonon process, developed by Huang and others, is generalized in this paper to consider both the radiative and nonradiative transitions between multielectron states, consistent with different symmetry-broken lattice configurations. The probability of the nonradiative decay of electron-hole pairs into soliton pairs and that of an electron (hole) into a polaron, as well as the cross section of soliton-pair photogeneration are calculated explicitly. The selection rules for both radiative and nonradiative transitions, and also the branching ratio of photoinduced neutral to charged solitons, are discussed. The theoretical results obtained are compared with numerical calculations and recent photoconductivity experiment.