Localized excitations and vibrational modes in a polyacene chain

By using an extended Su-Schrieffer-Heeger model, we investigate the localized elementary excitation and the vibrational modes in a polyacene chain, which is composed of finite-number aromatic rings. It is found that there exists an interchain-coupled neutral soliton in a pristine chain. Around the neutral soliton, there are nine vibrational modes, four are infrared-active and five are Raman-active.