Berlin 2001 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 10: Ultrafast Spectroscopy

CPP 10.5: Vortrag

Donnerstag, 5. April 2001, 17:05–17:25, 110

Femtosecond time resolved spectroscopy of acetanilide — •Julian Edler and Peter Hamm — Max-Born-Institut, Max-Born-Str. 2a, 12487 Berlin

Acetanilde(ACN) forms crystals with chains of hydrogen-bonded amide groups and can therefore be considered a model system for comparable structures in α-helices. The infrared absorbtion spectrum shows anomalities in the region of the amide-I and the N-H stretching band [1]. These anomalous bands have been explained by the coupling of these states to phonons, which leads to a self localization of the vibrational exciton [2].

We have used methods of nonlinear spectroscopy to investigate closer the mechanism which gives rise to the anomalities of the N-H band. Pump-probe experiments have shown, that the substate with the highest frequency (3300 cm ⁻¹ ) decays very fast, while the states with lower frequencies are stable on a > 10 ps timescale. We have also seen oscillations, which are explained by coherent excitation of the coupled phonon.

[1] G.Careri, U. Buontempo, F. Galluzzi, A. C. Scott, E. Gratton, E. Shyamsunder, Phys. Rev. B 30, 4689 (1984)

[2] D. M. Alexander and J. A. Krumhansl, Phys. Rev. B 33, 7172 (1986)