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O: Fachverband Oberflächenphysik

O 4: Solid-Liquid Interfaces: Structure

O 4.8: Vortrag

Montag, 17. März 2025, 12:15–12:30, H4

Exploring Charged Aqueous Interfaces with Depth-Resolved SFG/DFG Vibrational Spectroscopy — •Sarabjeet Kaur, Álvaro Díaz Duque, Alexander Fellows, Martin Wolf, and Martin Thämer — Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society

Charged aqueous interfaces are crucial in biological, atmospheric, and chemical processes, where surface electric fields influence ion distributions and interfacial dynamics. Water mediates these interactions, with effects spanning nanometers. The Gouy-Chapman (GC) model and variants describe ion distributions but oversimplify water as a continuous medium, neglecting molecular-level behaviors like impact of structure, orientation, and hydrogen-bonding dynamics. This omission leaves important aspects of interfacial phenomena unexamined. We address these gaps using depth-resolved vibrational spectroscopy combining phase-resolved sum- and difference-frequency generation (SFG and DFG). This technique reveals depth-dependent water responses and connects electric potential anisotropy with molecular reorientation. Our findings identify two distinct interfacial layers, challenging the single-layer GC model. Spectral analysis shows structural differences between the compact and diffuse layers. Additionally, concentration-dependent studies highlight discrepancies between the observed decay length of orientational anisotropy and the predicted Debye length. These results underscore the limitations of the GC variant model and continuum solvent approaches in capturing water's molecular-level behavior at charged interfaces.

Keywords: Charged interfaces; water structure; SFG/DFG spectroscopy; molecular level; Gouy-chapman model