Optical line shapes of dimers and molecular chains: Influence of a heat bath with coloured noise

Abstract

Optical absorption line shapes of electronic excitations in dimers and molecular chains are calculated. The interaction with phonons is described by dichotomic and Gaussian stochastic processes with exponentially decaying correlation functions (coloured noise) generalizing in this way the Haken-Strobl-Reineker treatment. For dimers with dichotomic fluctuations of the excitation energy a closed system of equations is obtained and the line shape can be determined exactly. In the case of Gaussian fluctuations an approximate treatment is used, which, when applied to dichotomic fluctuations, can be compared with the exact solution. The line shape for electronic excitations on a linear chain is calculated within this approximation scheme for Gaussian fluctuations. It is shown that the line shapes are asymmetric for slow fluctuations and symmetric in the case of last fluctuations.