Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 60: Chemistry at Solid/Liquid Interfaces
O 60.3: Talk
Wednesday, March 9, 2016, 15:45–16:00, S052
Molecular dynamics simulations of the libration region of the SFG spectra at the water-air interface. — •Rémi Khatib1, Taisuke Hasegawa2, Marialore Sulpizi1, Ellen H. G. Backus3, Mischa Bonn3, and Yuki Nagata3 — 1Institute of Physics, Johannes Gutenberg University, Mainz, Germany — 2Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Japan — 3Department for Molecular Spectroscopy, Max Planck Institute for Polymer Research, Mainz, Germany
Sum-frequency generation spectroscopy (SFG) has been used to probe interfacial water structure. Former studies of the stretching and bending modes have evidenced, that non-hydrogen-bonded O-H groups are present at the water-air interface.[1,2] In contrast, the low-frequency librational mode has been much less studied.
In this study, we compute the SFG spectrum at the water-air interface in the libration region by using molecular dynamics simulations. We show that the modelling of the polarizability for the optical response calculation has a drastic effect on the simulated spectra, while force field and dipole models have a minor impact. At the water-air interface, the neighbouring hydrogen-bond partner affects the polarizability in a very heterogeneous way, which cannot be captured with a single point polarizability model per water molecule. In the simulated spectra, the peak of the librational contribution to the imaginary part of the response is centred at 660 - 750 cm−1.
[1] Du, Q. et al., Phys. Rev. Lett., 1993, 70, 2313-2316. [2] Nagata, Y. et al., J. Phys. Chem. Lett., 2013, 4, 1872-1877