Peter Hamm
Department of Chemistry, University of Zurich, Switzerland
We have recently measured the 2D-Raman-THz signal of neat water as a function of temperature and isotope constitution [1], as well as that of aqueous salt solutions with a series of different salts [2]. We consider a short-lived echo the most important result of these experiments. The echo is a measure of the inhomogeneous broadening of the intermolecular modes of water, and hence a measure of the structural heterogeneity of the hydrogen-bond networks of water. However, the nature of the 2D-Raman-THz response is currently not well understood. I will discuss our theoretical efforts, based either on atomistic molecular dynamics simulations [3,4] or on effective models [5], to simulate these echoes, and hence to learn how to extract microscopic information from the experimental signals.
[1] A. Berger, G. Ciardi, P. Hamm and A. Shalit, The Impact of Nuclear Quantum Effects on the Structural Inhomogeneity of Liquid Water, Proc. Natl. Acad. Sci. USA, 2019, 116, 2458
[2] A. Shalit, S. Ahmed, J. Savolainen, and P. Hamm THz echoes reveal the inhomogeneity of water in aqueous salt solutions, Nature Chem., 2017, 9, 273
[3] P. Hamm 2D-Raman-THz spectroscopy: A sensitive test of polarizable water models J. Chem. Phys., 2014, 141, 184201
[4] P. Hamm, Velocity Echoes in Water, in preparation
[5] D. Sidler, P. Hamm, Feynman Diagram Description of 2D-Raman-THz Spectroscopy Applied to Water, J. Chem. Phys. 2019, 150, 044202