Dresden 2017 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 33: Fluid Dynamics and Turbulence

DY 33.10: Talk

Wednesday, March 22, 2017, 12:30–12:45, ZEU 160

intermolecular mode coupling: insight from nonlinear THz spectroscopy of liquids — •mohsen sajadi, martin wolf, and tobias kampfrath — fritz-haber-institute of the max-planck society, berlin, germany

Low-frequency structural dynamics of liquids in the range of 0.1 to 10 THz (3 to 300 cm-1 ) is believed to strongly contribute to the outcome of chemical processes. The underlying molecular motions are very complex and include reorientations, vibrations and translations. Implemented techniques for gaining microscopic insight to such low-frequency molecular motions have mostly been limited to the off-resonant optical excitation of liquids via Raman processes. Using intense THz fields, we interrogate the structural dynamics of molecular liquids directly. We show that resonant excitation with strong THz pulses is capable of driving librational-reorientational modes of liquids through coupling to the permanent molecular dipole moments. We observe a hallmark of this light-matter interaction as a transient optical birefringence up to one order of magnitude higher than obtained with optical excitation. In light of a simple but generic model and excitation at different THz frequencies we discuss that the enhancement arises from resonantly driven librations and their coupling to reorientational motion, assisted by either the pump field or a cage translational mode.