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MO: Molekülphysik
MO 12: Posters Friday: Spectroscopy
MO 12.11: Poster
Friday, April 6, 2001, 12:30–15:00, AT3
Selective Excitation of Vibrational Modes in the Electronic Ground State of Polydiacetylenes — •Felix Busch, Tao Chen, Achim Vierheilig, Wolfgang Kiefer, and Arnulf Materny — Institut für Physikalische Chemie, Am Hubland, D-97074 Würzburg, email: amaterny@phys-chemie.uni-wuerzburg.de
In this contribution, we report the controlled selective excitation of vibrational modes in the electronic ground state of polymers of diacetylenes (PDAs). The technique applied to exciting and probing is femtosecond time-resolved four-wave mixing spectroscopy with broad-band detection. A coherent anti-Stokes Raman scheme is used, where the difference of pump and Stokes laser wavelengths is chosen to achieve resonance with several chain modes of the polydiacetylenes. The control of mode excitation was performed in two ways. First, the delay time τ1 between pump and Stokes laser pulses was varied for laser pulses having minimized chirp. In this case, the dynamics on the electronically excited potential energy surface determined the optimal overlap to certain vibrational modes in the electronic ground state of the PDAs. Second, we have changed the phase shape (chirp) of the exciting laser pulses. This method is of great interest as here not necessarily the dynamics in the electronically excited states have to be included. Using these two methods, we were able to strongly influence the dynamics and intensity of the coherently excited ground state modes of the PDAs.