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MO: Fachverband Molekülphysik
MO 9: Femtosecond Spectroscopy II
MO 9.5: Talk
Tuesday, March 15, 2011, 11:45–12:00, TOE 317
Ultrafast Dynamics of N-H Stretching Excitations of Guanosine-Cytidine Base Pairs in Solution — •Ming Yang1, Łukasz Szyc1, Katharina Röttger2, Henk Fidder1, Erik T. J. Nibbering1, Thomas Elsaesser1, and Friedrich Temps2 — 1Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Str. 2A, 12489 Berlin, Germany — 2Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24098 Kiel, Germany
In DNA hydrogen bonds (h-bonds) between the nucleobases play a key role. We study the N-H stretching vibrations of h-bonded guanosine-cytidine (GC) base pairs in chloroform solution with linear and ultrafast nonlinear infrared (IR) spectroscopy. We assign the IR-active transitions by combining structural information on the h-bonds in the GC pairs with literature on DFT calculations, and empirical relations connecting frequency shifts and intensities of the IR-active vibrations. We adopt a model of local five N-H stretching vibrations, describing motions of free NH groups of G and C, and h-bonded NH groups between G and C, to interpret the femtosecond two-dimensional (2D) photon echo and pump-probe measurements in terms of couplings and relaxation dynamics. The free N-H stretching vibrations of G and C have a population lifetime of 2.4 ps. Besides a vibrational population lifetime shortening to subpicosecond values observed for the h-bonded N-H stretching vibrations, the 2D spectra reveal vibrational excitation transfer from the 3303 cm−1 G(NH2) to the 3145 cm−1 G(N-H⋯N)and C(NH2) modes on a time scale of 1 ps.