Hamburg 2009 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 7: Femtosekundenspektroskopie 1
MO 7.4: Vortrag
Dienstag, 3. März 2009, 11:15–11:30, VMP 6 HS-F
Ultrafast vibrational wavepacket motions in 2-pyridone dimers — •Ming Yang, Łukasz Szyc, Jens Dreyer, Erik T. J. Nibbering, and Thomas Elsaesser — Max-Born-Institute, D-12489 Berlin, Germany
Hydrogen-bonded N-H groups are ubiquitous in nature, playing a key role in the nucleic acid base pairing in DNA and RNA, and in the secondary structure of proteins. Here, a nitrogen atom donates a hydrogen to an accepting electronegative oxygen or nitrogen. The infrared-active N-H stretching band displays key signatures such as frequency downshifts, line broadening and distinct band substructures providing direct access to the the hydrogen bond strength and anharmonic vibrational mode couplings. Here we present recent results obtained on the hydrogen-bonded 2-pyridone dimer in nonpolar solution, a model system for DNA nucleic base pairing. In femtosecond infrared pump-probe experiments on the N-H stretching band we determine the population decay of the N-H stretching vibration to occur with a 200 fs time constant. Superimposed on the population dynamics of the N-H stretching vibration we observe coherent oscillations indicative of coherent wavepacket motions of the dimer in-plane bending and dimer stretching modes, with respective eigenfrequencies of 100 and 160 cm−1. These low-frequency vibrational modes, strongly affecting the hydrogen bond distance, are anharmonically coupled to the N-H stretching vibration, and as such are coherently driven and read out by the ultrashort infrared pulses tuned at the N-H stretching band.