Vibronic Coupling. II. Spectra of Dimers

Abstract

We consider a model dimer composed of units with one allowed excited state and one symmetric vibration. The vibrational mode has the same force constant in the ground and excited states, but the excited state is assumed to have its equilibrium position shifted by an amount measured by λ. The dimer possesses a symmetry operation that exchanges the units and has an exciton coupling ε. Spectra for various λ and ε values are derived by computer. It is shown that the absorption intensity of the two polarizations rigorously satisfies two theorems: the center of gravity is at ±ε for all λ; the bandwidth is | λ | for all ε.