"Nonlinear THz Spectroscopy of liquids: Energy Transfer within the Hydrogen Bonding Network of Water"

Vous êtes cordialement invités à la conférence de Mohsen Sajadi, Fritz-Haber-Institute of the Max-Planck Society, Berlin, Germany, organisée par l'IPCMS

Resumé:

Terahertz (THz) radiations are highly relevant for basic research and spectroscopy as many resonances of
physical systems lie at THz frequency range.1 Liquid water is an example of such molecular systems with
very rich THz dynamics. Interestingly, the low-frequency THz dynamics of water are believed to strongly
contribute to the bio-chemical reactivity of this liquid.2 However, linear spectroscopies such as dielectric
relaxation3 and even nonlinear multidimensional optical spectroscopies, such as photon echo4 showed limited
power to provide a detailed understanding of the intermolecular interactions in liquid water.
To this end, we seek the nonlinear response of water after resonant THz excitation of its intermolecular
degrees of freedom. Here, I report a THz pump-optical probe experiment and address the dynamic energy
flow in the hydrogen-bond network of water. Complementary gas-phase and optical experiments declare
that the THz electric field couples to the molecular rotations and its energy is rapidly transferred to the restricted-
translational motion of neighboring water molecules.5 This rapid energy transfer may only be rationalized
by a strong anharmonicity of the intermolecular interactions.
I will also discuss few examples in which intense THz electromagnetic waves have been used for resonant
excitation of phonons and/or magnons in solids.
1. R. Ulbricht et al., Rev. Mod. Phys. 83, 543 (2011).
2. K. J.Tielrooij, et al., Science 328, 1006 (2010).
3. T. Fukasaw et al., Phys. Rev. Lett. 95, 197802 (2005).
4. A. Tokmakoff et al., J. Chem. Phys. 103, 2810 (1995).
5. M. Sajadi, et al., Nat. Commun. 8, (2017).
Contact: Pascal Hébraud: pascal.hebraud@ipcms.unistra.fr