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10:28
Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy
Published on: May 27, 2018
Structural rearrangements in water viewed through two-dimensional infrared spectroscopy
Sean T Roberts1, Krupa Ramasesha, Andrei Tokmakoff
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Accounts of Chemical Research
|July 10, 2009
Summary
Researchers used ultrafast 2D IR spectroscopy to study liquid water's structure. They found that broken hydrogen bonds rapidly reorient, revealing insights into water's dynamic hydrogen-bond rearrangements.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Molecular Dynamics
Background:
- Water's unique structure arises from hydrogen bonding, forming a dynamic tetrahedral network.
- Understanding water's ultrafast molecular motions is crucial for chemical and biological processes.
- Previous methods lacked the temporal resolution to capture rapid hydrogen-bond dynamics.
Purpose of the Study:
- To investigate the mechanism of hydrogen-bond rearrangements in liquid water.
- To utilize ultrafast two-dimensional infrared (2D IR) spectroscopy to track time-dependent structural changes.
- To interpret 2D IR spectra using molecular dynamics simulations for atomistic insights.
Main Methods:
- Employed two-dimensional infrared (2D IR) spectroscopy on dilute HOD in D(2)O to monitor OH stretching frequencies.
- Utilized advanced molecular dynamics simulations to calculate 2D IR spectra and interpret experimental data.
- Analyzed spectral broadening and frequency evolution to understand molecular reorientation dynamics.
Main Results:
- Observed asymmetric 2D IR spectra, with broadening in the weak/broken hydrogen bond region (>3500 cm(-1)) on a ~60 fs timescale.
- This broadening indicates rapid reorientation of molecules with unstable hydrogen bonds.
- Simulations revealed large-angle molecular reorientations and a bifurcated hydrogen bond transition state during exchange.
Conclusions:
- Ultrafast 2D IR spectroscopy combined with simulations provides a detailed understanding of liquid water dynamics.
- Hydrogen-bond exchange involves correlated motions of multiple water molecules, extending to the second solvation shell.
- 2D IR spectroscopy can serve as a transition-state spectroscopy if a spectral signature exists.
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