Water vibrational spectroscopy

Raduge C, Pfiumio V and Shen Y R 1997 Surface vibrational spectroscopy of sulfuric acid-water mixtures at the liquid-vapor interface Chem. Phys. Lett. 274 140... 

Shen Y R 1998 Sum frequency generation for vibrational spectroscopy applications to water interfaces and films of water and ice Solid State Commun. 108 399... 

We now present one of the many examples of interfacial vibrational spectroscopy using SFG. Figure Bl.5.15 shows the surface vibrational spectrum of the water/air interface at a temperature of 40 °C [83]. Notice that... 

Du Q, Superfine R, Freysz E and Shen Y R 1993 Vibrational spectroscopy of water at the vapor-water interface Phys. Rev. Lett. 70 2313-16... 

If H2 80 is used in the reaction, the label can be followed. After the products are separated, vibrational spectroscopy or mass spectrometry can be used to determine whether the product has incorporated the l8(). If an O atom came from the water, the molar mass of the methanol produced would be 34 g-mol", not 32 g-mol. ... 

Taking into consideration that antenna xanthophylls not only possess original absorption but also resonance Raman spectra, and the fact that the Raman signal is virtually free from vibrational spectroscopy artifacts (water, sample condition, etc.), it seemed of obvious advantage to apply the described combination of spectroscopies for the identification of these pigments. 

About one decade ago Bass et al. [13,14] proposed first that such approach could help in exploring the structure of water dissolved silicates. Following this initiative, recently we critically evaluated how the published FTIR and Raman assignments could be adopted for differentiating between the molecular structures of some commercially available sodium silicate solutions [7-9,15], In this paper we present comparative structural studies on aqueous lithium and potassium silicate solutions as well. According to some NMR studies, the nature of A+ alkaline ion and the A+/Si ratio barely affects the structural composition of dissolved silicate molecules [5], In contrast, various empirical observations like the tendency of K-silicate solutions to be less tacky and more viscous than their Na-silicate counterparts, the low solubility of silica films obtained from Li-silicate solutions compared to those made from other alkaline silicate solutions, or the dependence of some zeolite structures on the nature of A+ ions in the synthesis mixture hint on likely structural differences [16,17]. It will be shown that vibrational spectroscopy can indeed detect such differences. 

The use of neutron reflectivity at liquid interfaces, which is a method sensitive to both surface roughness and surfactant layer thickness, was reviewed with the examples of polydimethylsiloxane-surfactant layers.633 Sum-frequency generation (SFG) vibrational spectroscopy was applied to study surface restructuring behavior of PDMS in water in an attempt to understand antifouling properties of silicones.6 ... 

Vibrational spectroscopy can help us escape from this predicament due to the exquisite sensitivity of vibrational frequencies, particularly of the OH stretch, to local molecular environments. Thus, very roughly, one can think of the infrared or Raman spectrum of liquid water as reflecting the distribution of vibrational frequencies sampled by the ensemble of molecules, which reflects the distribution of local molecular environments. This picture is oversimplified, in part as a result of the phenomenon of motional narrowing The vibrational frequencies fluctuate in time (as local molecular environments rearrange), which causes the line shape to be narrower than the distribution of frequencies [3]. Thus in principle, in addition to information about liquid structure, one can obtain information about molecular dynamics from vibrational line shapes. In practice, however, it is often hard to extract this information. Recent and important advances in ultrafast vibrational spectroscopy provide much more useful methods for probing dynamic frequency fluctuations, a process often referred to as spectral diffusion. Ultrafast vibrational spectroscopy of water has also been used to probe molecular rotation and vibrational energy relaxation. The latter process, while fundamental and important, will not be discussed in this chapter, but instead will be covered in a separate review [4],... 

As described above, it is probably adequately clear that the vibrational spectroscopy of water is complicated indeed One can simplify the situation considerably by considering dilute isotopic mixtures. Thus one common system is dilute HOD in D2O. The large frequency mismatch between OH and OD stretches now effectively decouples the OH stretch from all other vibrations in the problem, meaning that the OH stretch functions as an isolated chromophore. Of course the liquid is now primarily D2O instead of H2O, which has slightly different structural and dynamical properties, but that is a small price to pay for the substantial simplification this modification brings to the problem. 

As discussed earlier, vibrational spectroscopy in neat water is much more complicated, due to the effects of both intramolecular and intermolecular coupling between OH stretch chromophores. 

Another theoretical frontier involves the study of the vibrational spectroscopy of water at other conditions, or in other phases. Here it will be crucially important to use more robust water models, since many effective two-body simulation models were parameterized to give agreement with experiment at one state point room temperature and one atmosphere pressure. We have already seen that using these models at higher or lower temperatures even for liquid water leads to discrepancies. We note that a significant amount of important theoretical work on ice has already been published by Buch and others [71, 72, 111, 175, 176]. 

How one obtains the three normal mode vibrational frequencies of the water molecule corresponding to the three vibrational degrees of freedom of the water molecule will be the subject of the following section. The H20 molecule has three normal vibrational frequencies which can be determined by vibrational spectroscopy. There are four force constants in the harmonic force field that are not known (see Equation 3.6). The values of four force constants cannot be determined from three observed frequencies. One needs additional information about the potential function in order to determine all four force constants. Here comes one of the first applications of isotope effects. If one has frequencies for both H20 and D20, one knows that these frequencies result from different atomic masses vibrating on the same potential function within the Born-Oppenheimer approximation. Thus, we... 

The non-destructive character of vibrational spectroscopy techniques, such as NIR, makes them novel tools for in-line quality assurance (100). NIR has been widely used for the measurement of water in various applications (101). NIR can be applied for both quantitative analysis of water and for determining the state of water in solid material. This gives a tool for understanding the physicochemical phenomena during manufacture of pharmaceutical granulation. 

Water is an interesting and important liquid. As the combination of multidimensional vibrational spectroscopy and molecular dynamics helps us understand water better, more and more complex dynamics have been revealed [8,9]. We can briefly explain why a liquid of triatomic molecules turns out to be so immensely complicated Water s three atoms bestow all the complexity of multiple intramolecular vibrations, and in addition in water there are more hydrogen bonds (—3.57) than atoms ... 

When an electron is injected into a polar solvent such as water or alcohols, the electron is solvated and forms so-called the solvated electron. This solvated electron is considered the most basic anionic species in solutions and it has been extensively studied by variety of experimental and theoretical methods. Especially, the solvated electron in water (the hydrated electron) has been attracting much interest in wide fields because of its fundamental importance. It is well-known that the solvated electron in water exhibits a very broad absorption band peaked around 720 nm. This broad absorption is mainly attributed to the s- p transition of the electron in a solvent cavity. Recently, we measured picosecond time-resolved Raman scattering from water under the resonance condition with the s- p transition of the solvated electron, and found that strong transient Raman bands appeared in accordance with the generation of the solvated electron [1]. It was concluded that the observed transient Raman scattering was due to the water molecules that directly interact with the electron in the first solvation shell. Similar results were also obtained by a nanosecond Raman study [2]. This finding implies that we are now able to study the solvated electron by using vibrational spectroscopy. In this paper, we describe new information about the ultrafast dynamics of the solvated electron in water, which are obtained by time-resolved resonance Raman spectroscopy. 

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