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Bonn 2000 – scientific programme

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MO: Molekülphysik

MO 20: Poster II: Ultraschnelle Dynamik

MO 20.3: Poster

Thursday, April 6, 2000, 17:00–19:30, Aula

Study of the phonon dynamics in the electronic ground state of polydiacetylenes with frequency–resolved femtosecond CARS — •T. Chen, A. Vierheilig, P. Waltner, A. Materny, and W. Kiefer — Institut für Physikalische Chemie der Universität Würzburg, Am Hubland, 97074 Würzburg

Frequency–resolved femtosecond CARS was applied to polydiacetylenes to investigate the dynamics of phonons of different vibrational modes in the electronic ground state.
At time zero one pump and the Stokespulses prepare a wave packet composed of several phonon modes in the electronic ground state. In the experiments presented, these are ν2, ν3 and ν4. After a time delay τ2 the wave packet is probed by the second pump pulse. The anti-Stokes signal is dispersed in a spectrometer and detected by an optical multichannel analyzer (OMA) to yield information about the contribution of the three coherently excited modes. When the delay time between the first pump and Stokes pulses is negative or the wave-vector difference of the first pump and Stokes lasers is vertical to the backbone of the polydiacetylenes, the signal corresponding to the ν3 and ν4 modes is stronger. When the delay time between the first pump and Stokes pulses is positive or the wave-vector difference of the first pump and Stokes lasers is parallel to the backbone of the polydiacetylenes, the signal corresponding to the ν2 mode is dominant. We discuss a possible application for the optimation of the generation of the coherent population in different vibrational states of polyatomic molecules. Relaxation times and intramolecular vibrational energy redistribution(IVR) are analyzed.

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