Abstract
We study the molecular-level properties of the single-crystal ice Ih surface using interface-specific sum frequency generation spectroscopy. We probe the water vibrational bend region around 1650 cm–1 of the basal plane of hexagonal ice to understand the interfacial structure from vibrational properties. As opposed to the stretch mode of ice, the bending mode response depends very weakly on temperature. The large line width of the bending mode response, relative to the response on water, is inconsistent with inhomogeneous broadening and points to ultrafast pure dephasing. The bending mode of ice provides an excellent means to study adsorbate–ice interactions and understand differences in ice and water reactivity.
Highlights
The water−air and ice−air interfaces act as active sites for chemical reactions in both natural and engineering settings
Information on the molecular properties of the interface can be obtained with surfacespecific vibrational spectroscopic methods, such as sum frequency generation (SFG) spectroscopy.[11,12]
The stretch mode spectrum is dominated by a signal at roughly 3200 cm−1 assigned to O−H modes hydrogen-bonded to neighbors
Summary
The water−air and ice−air interfaces act as active sites for chemical reactions in both natural and engineering settings. The properties of interfacial water molecules have been extensively studied owing to their relevance in atmospheric,[1,2] biological,[3] electrochemical,[4,5] and geological sciences.[6] Ice interfaces have raised particular scientific interest owing to their reported high catalytic activity[7,8] and implications in frost heave, supraglacial chemistry,[9] and exchange of trace gases establishing atmospheric concentrations of species.[10] Information on the molecular properties of the interface can be obtained with surfacespecific vibrational spectroscopic methods, such as sum frequency generation (SFG) spectroscopy.[11,12] As a secondorder nonlinear technique, SFG is inherently interface-specific owing to its selection rule that inversion symmetry must be broken for the signal to be generated In this method, two laser beams, an infrared beam in resonance with a vibrational transition, and a visible beam for upconversion are overlapped in space and time. The SFG intensity as a function of infrared frequency provides the vibrational spectrum of the interfacial molecules
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