Hamburg 2009 – scientific programme
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MO: Fachverband Molekülphysik
MO 4: Verschiedenes
MO 4.1: Talk
Monday, March 2, 2009, 17:00–17:15, VMP 6 HS-F
J- and H-bands of molecular aggregates: validity of the CES approximation — •Jan Roden1, Alexander Eisfeld1, and John Briggs2 — 1MPIPKS Dresden — 2Uni Freiburg, Theoretische Quantendynamik
In molecular aggregates collective excitations of the constituting monomers lead to the formation of a narrow red-shifted absorption peak, the J-band, and a broad blue-shifted band with a lot of structure, the H-band [1]. Due to strong coupling to vibrations the understanding of the details of the aggregate absorption spectrum remains a difficult task. However, the "coherent exciton scattering" (CES) approximation is able to well reproduce the measured bandshapes of both the J- and the H-band in detail by taking the experimental spectrum of a single molecule as input. To better understand the excellent agreement of CES calculations and measured aggregate spectra and to investigate the validity of the CES approximation a comparison with direct diagonalisation of a model vibronic Hamiltonian, where only one undamped vibrational mode is taken into account, is performed [2]. Only in the H-band region, where previously good agreement of CES and measured spectra was obtained [3], CES does not conform to the direct diagonalisation spectra. This is shown to arise from use of the measured monomer spectrum which includes implicitly dissipative effects not present in the model calculation.
[1] T. Kobayashi, J-Aggregates, World Scientific, 1996
[2] J. Roden, A. Eisfeld, J. S. Briggs, Chem. Phys. 352 (2008) 258
[3] A. Eisfeld, J. S. Briggs, Chem. Phys. 324 (2006) 376