Abstract
The interaction between intramolecular and intermolecular degrees of freedom in liquid water underlies fundamental chemical and physical phenomena such as energy dissipation and proton transfer. Yet, it has been challenging to elucidate the coupling between these different types of modes. Here, we report on the direct observation and quantification of the coupling between intermolecular and intramolecular coordinates using two-dimensional, ultra-broadband, terahertz-infrared-visible (2D TIRV) spectroscopy and molecular dynamics calculations. Our study reveals strong coupling of the O-H stretch vibration, independent of the degree of delocalization of this high-frequency mode, to low-frequency intermolecular motions over a wide frequency range from 50 to 250 cm−1, corresponding to both the intermolecular hydrogen bond bending (≈ 60 cm−1) and stretching (≈ 180 cm−1) modes. Our results provide mechanistic insights into the coupling of the O-H stretch vibration to collective, delocalized intermolecular modes.
Highlights
The interaction between intramolecular and intermolecular degrees of freedom in liquid water underlies fundamental chemical and physical phenomena such as energy dissipation and proton transfer
We use a spectrometer and camera to measure the four-wave mixing (FWM) light emitted by the sample and employ heterodyne detection, allowing us to measure the electric field of the signal rather than its intensity
We develop a two-dimensional terahertz-infraredvisible (2D TIRV) spectroscopy, which can directly measure the coupling between the lowfrequency modes (LFM) and high-frequency intramolecular modes (HFM) vibrations
Summary
The interaction between intramolecular and intermolecular degrees of freedom in liquid water underlies fundamental chemical and physical phenomena such as energy dissipation and proton transfer. Note 1) THz pulse laser-generated in air plasma[34,35,36] creates a vibrational coherence state in a sample by excitation of its LFM (Fig. 2d). This process makes up the well-known four-wave mixing (FWM). The generation of the FWM signal is enhanced when states |1〉, |2〉, and |3〉
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