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Hydrogen order at the surface of ice I <sub/>h</sub> revealed by vibrational spectroscopy
摘要： Among numerous crystalline phases of ice, the Ih phase is the most stable above 72 K at atmospheric pressure. It is well established that the orientations of water molecules in the bulk of ice Ih are statistical without long-range order. However, the orientational order of water at the surface of ice Ih has been enigmatic. Here we show that the surface of ice Ih at 100 K has hydrogen order with the OH group pointing upward to the air (‘‘H-up’’ orientation). We applied nonlinear optical spectroscopy and theoretical modeling to the surface of isotopically pure and diluted ice Ih and observed OH stretch vibrational signatures attributed to H-up ordering. Furthermore, we found that this hydrogen order takes place despite a more inhomogeneous microenvironment at the surface than in the bulk. Our results suggest the prominent role of the surface to allow the reorientation of water molecules for hydrogen ordering that is virtually prohibited in the bulk.
关键词： surface structure,ice Ih,hydrogen order,nonlinear optical spectroscopy,vibrational spectroscopy
更新于2025-09-23 15:19:57
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Four-Dimensional Coherent Spectroscopy of Complex Molecular Systems in Solution
摘要： An understanding of microscopic interactions in solution is of fundamental importance in chemistry. However, the structure and dynamics of complex systems in the condensed phase, especially far from thermal equilibrium, are masked by broad and often featureless absorption and emission spectra. Nonlinear optical spectroscopy has proven to be a powerful and general approach to disentangling congested spectra by spreading information across multiple dimensions, revealing features oftentimes hidden in lower-order projections. As the dimensionality of the measurement increases, the better the microscopic interactions are revealed as spectral bands disperse in the large hyper-spectral volume. This capability, however, comes at a steep price as the signal decreases exponentially at higher orders of optical response and added experimental complexity increases noise. Here, we discuss a four-dimensional coherent spectroscopy known as Gradient Assisted Multidimensional Electronic–Raman Spectroscopy (GAMERS) that reveals coupling between electronic and vibrational transitions in complex, condensed phase systems ranging from organic molecules to semiconductor nanocrystals. We reveal that high-resolution spectra may be extracted from these systems even in the presence of severe spectral broadening, both homogeneous and inhomogeneous in origin. The theoretical and experimental underpinnings of this method are discussed. Increasingly, higher-order and higher-dimensionality spectroscopies like GAMERS are needed to understand the microscopic interactions that connect structure to dynamics to function.
关键词： condensed phase,GAMERS,complex systems,electronic and vibrational transitions,Nonlinear optical spectroscopy
更新于2025-09-10 09:29:36