Hamburg 2009 – scientific programme

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MO: Fachverband Molekülphysik

MO 7: Femtosekundenspektroskopie 1

MO 7.5: Talk

Tuesday, March 3, 2009, 11:30–11:45, VMP 6 HS-F

Vibrational relaxation after spectrally selective excitation in the structured N-H stretching band of 7-azaindole dimer — •Kozich Valeri, Dreyer Jens, and Werncke Wolfgang — Max-Born-Institut, Max-Born-Strasse 2A, D-12489 Berlin, Germany

The dimer of 7-azaindole may be regarded as a model system for the base pairs of DNA. Dimerization leads to formation of a highly structured N-H stretching band and an extreme shortening of the lifetime of this vibration. Here we report on investigations of mode-selectivity of vibrational redistribution after spectrally selective excitation within the N-H stretching band by sub-picosecond infrared-pump/anti-Stokes resonance Raman-probe spectroscopy. Generally our measurements indicate ultrafast initial population transfer to fingerprint vibrations with N-H bending character. Subsequently the energy is transferred to modes with lower frequencies. The infrared excitation at different substructures of the N-H stretching band clearly influences the distribution of populations between the different fingerprint modes. Their relative populations correlate with the contribution of the modes to various combination tones coupled to the N-H stretching vibration. Our results provide experimental support to a Fermi resonance model used for modeling the IR spectrum of the N-H stretching band and give insight into relaxation processes and energy redistribution. Relaxation to distinct vibrational fundamentals contributing to the combination bands forming the initially excited sub-band is strongly favoured.