Excited states and their relaxation dynamics intrans-polyacetylene

We investigate excited states in polyacetylene, taking account of electron correlation by transforming the electronic degrees of freedom into a quantum phase variable via boson representation. When the lattice is fixed at the ground-state configuration, there are the following species of excitations: soliton Sᵉ, antisoliton Sᵉ, the first breather B₁ᵉ, and the second breather B₂ᵉ. Sᵉ should not be confused with the usual neutral soliton S^e-l; in the former, the amount of phase change is 2{π} and the lattice is in the uniformly dimerized state, while in the latter the amount of phase change is {π} and the lattice has a usual soliton structure. Sᵉ, B₁ᵉ, and Sᵉ are three components of the triplet exciton, and B₂ᵉ is the singlet dipole-forbidden exciton which corresponds to the 2 ¹Ag state in finite polyenes. The electronic structure of B₂ᵉ can be regarded as a bound state of S^e-l's. We study the dynamics of the lattice relaxation from B₂ᵉ by applying a semiclassical approximation to the boson system. Since the lattice is driven by the electronic structure of B₂ᵉ, a neutral soliton pair or their bound state is formed as a relaxation product.