We study the bending mode of pure water and charged aqueous surfaces using heterodyne-detected vibrational sum-frequency generation spectroscopy. We observe a low (1626  cm−1) and a high (1656  cm−1) frequency component that can be unambiguously assigned to an interfacial dipole and a bulk quadrupolar response, respectively. We thus demonstrate that probing the bending mode provides structural and quantitative information on both the surface and the bulk.

The Netherlands Organisation for Scientific Research (NWO) , European Research Council (ERC) , European Union Horizon 2020
Ultrafast Spectroscopy

Moll, C.J, Versluis, J, & Bakker, H.J. (2021). Direct Evidence for a Surface and Bulk Specific Response in the Sum-Frequency Generation Spectrum of the Water Bend Vibration. Phys.Rev.Lett., 127(11), 116001: 1–116001: 6. doi:10.1103/physrevlett.127.116001