Münster 1999 – wissenschaftliches Programm

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CP: Chemische Physik

CP 7: Spektroskopie

CP 7.7: Vortrag

Montag, 22. März 1999, 15:30–15:45, Gg

Excitd state absorption of molecular aggregates: influence of exciton-exciton interaction and higher molecular levels — •P. Reineker¹ and G. Juzeliunas^1,2 — ¹Abteilung Theoretische Physik, Universit"at Ulm, 89069 Ulm — ²Institute of Theoretical Physics and Astronomy, A. Gostato 12, Vilnius 2600, Lithuania

The differential pump-probe spectrum for excitons in linear molecular aggregates has been considered taking into account both the influence of exciton-exciton interaction and of higher molecular levels. The theoretical analysis carried out in terms of the Green function technique provides analytical expressions for the lineshape of the pump-probe spectrum valid for an arbitrary number N of molecules. In addition, the theory can accomodate any number of molecular states with higher energies, including the situation in which higher-lying states are charactrized by a dense set of sublevels of electronic, vibrational, etc. origin. It is demonstrated that incorporation of such higher molecular levels introduces widths to the biexciton peaks. Furthermore, the indirect interaction between the excitons via the higher molecular levels can facilitate formation of biexcitons at lower than usual values of the direct exciton-exciton coupling γ. Beyond the critical value of γ, corresponding to the formation of biexcitons, the differential spectrum can be described reasonably well in terms of the spectrum of non-interacting excitons subject to the replacement of the actual number of molecules per aggregate N by an effective one.