Speaker
Prof.
Peter Hamm
(University of Zurich)
Description
Water is a complex liquid due to the hydrogen-bond
network
that it forms. The associated low-frequency spectrum of
water reports directly on its thermally excited
intermolecular
degrees of freedom. In this frequency range, the
intermolecular spectrum of water consists of broad,
almost
featureless bands at ~600 cm-1 (hindered rotations),
~200
cm-1 (hydrogen bond stretching) and at ~60 cm-1
(hydrogen
bond bending). In order to resolve the lineshape
functions of
these modes as well as their couplings, a
multidimensional
spectroscopy directly in this frequency range is needed.
I will discuss 2D-Raman-THz spectra of liquid water as
one
such spectroscopy (see Fig. 1) [1]. In order to facilitate
the
interpretation of these experiments, all-atom molecular
dynamics simulations have been performed with various
polarizable models of water. It is found that the 2D-
Raman-
THz response depends extremely critically on the
description
of polarizability. From the models which have been
tested so
far, the best (but certainly not perfect) agreement with
experiment is obtained for the TL4P model, which has
recently been introduced by Tavan and coworkers [2].
[1] J. Savolainen, S. Ahmed and P. Hamm, “2D-Raman-
THz
Spectroscopy of Water” Proc. Natl. Acad. Sci. USA, 110
(2013) 20402
[2] P. Tröster, K. Lorenzen, M. Schwörer, and P. Tavan,
J.
Phys. Chem. B 117, 9486 (2013).
