Vibrational modes of water

Figure 1. Vibrational modes of water and a methylene group.

FIGURE 3.13 The three normal vibrational modes of water. For the top mode (the symmetric stretch) both O-H bonds are extended or compressed at the same time. For the middle mode (the antisymmetric stretch) one O-H bond is extended when the other is compressed. The bottom mode is called the bend. In every case the hydrogen atoms move more than the oxygen, because the center of mass has to stay in the same position (otherwise the molecule would be translating). For a classical molecule (built out of balls and perfect springs) these three modes are independent. Thus, for example, energy in the symmetric stretch will never leak into the antisymmetric stretch or bend modes. 

Our findings for rs and th may be compared with results of computer simulations for water. Values between 1 and 2 ps are stated for the average lifetime of a hydrogen bond by different authors (121-123), in satisfactory agreement with our experimental values. It is also interesting to compare with the frequency shift correlation function of the vibrational modes of water obtained from MD computations (124). Recently a slower component of this function with an exponential time constant of 0.8 ps was predicted for HDO in D20 at 300 K and a density of 1.1 g/cm3 (pressure %2 kbar). The existence of the slow component is a necessary prerequisite for the observation of spectral holes and the spectral relaxation time rs reported here. The faster component of the frequency shift correlation function with rc = 50 fs (124) represents rapid fluctuations that contribute to the spectral bandwidths of the spectral species and of the spectral holes. 

Symmetry can be helpful in determining the modes of vibration of molecules. Vibrational modes of water and the stretching modes of CO in carbonyl complexes are examples that can be treated quite simply, as described in the following pages. Other molecules can be studied using the same methods. 

Vibrational Modes of Water Molecules in Solid Hydrates - 106... 

Figure 1 Schematic representation of the behavior of the energy, hardness, and polarizability in the antisymmetric and symmetric stretching vibrational modes of water...

We know already that the chosen computational methods accurately describe the properties of pheuol, particularly its vibrational spectrum. The frequeucies of the OH stretchiug vibrations of phenol and water molecule are collected in Table 35. It is interesting to note that the HF/A frequency of 4118 cm" assigned to the vqh stretching vibration of bare phenol corresponds to its highest frequency. Therefore, it can be treated as the most accepting mode of phenol. Moreover, this frequency lies between the frequencies of the vi (4070 cm" ) and (4188 cm" ) OH-stretching vibrational modes of water molecules (equation 40),... 

Por solvation d)mamics of dipoles in pure water, experimental studies find a sub-50 fs Gaussian componenf, followed by a slow bi-exponential decay with time constants 126 and 880 fs, respectively (Jimenez et al., 1994). It is believed that the initial ultra-fast response comes from fhe intermolecular O- -O vibrational modes of water while the slowest one comes from the reorientational d3mamics of water (Roy and Bagchi, 1993 Nandi et al., 1995). The success in the investigation of solvation d)mamics in bulk water motivated many additional studies on complex systems where water is an... 

Water is dominant in the IR spectrum of swollen hydrogels. Figure 19a shows the ATR spectrum of water-containing PVP. The three strongest absorption bands are due to vibrational modes of water. The weak bands that are indicated by a star in Fig. 19a arise from PVP. The Raman spectrum of the same sample is represented in... 

Straus et al. [223] noticed that the quantization of the librational and vibrational modes of water (by means of the Feynman path integral formalism [224]) can significantly influence the solvent free energy barrier and the thermodynamic driving force of the heterogeneous electron transfer process. For more information the reader is referred to the cited publications and the references therein. 

Vibrational modes of water. Shown are the internal modes (a) symmetric stretch, (b) bending, (c) asymmetric stretch, and the librational modes (d) wag, (e) twist, and (f) rock. Not shown are the three hindered translational modes. 

Table 2 Vibrational Modes of Water in Varions Phases...

A key requirement for in-situ spectroscopic methods in these systems is surface specificity. At Uquid/Uquid junctions, separating interfacial signals from the overwhelmingly large bulk responses in linear spectroscopy is not a trivial issue. On the other hand, non-Unear spectroscopy is a powerful tool for investigating the properties of adsorbed species, but the success of this approach is closely linked to the choice of appropriate probe molecules (besides the remarkably sensitivity of sum frequency generation on vibrational modes of water at interfaces). This chapter presents an overview of linear and non-linear optical methods recently employed in the study of electrified liquid/liquid interfaces. Most of the discussion will be concentrated on the junctions between two bulk liquids under potentio-static control, although many of these approaches are commonly employed to study liquid/air, phospholipid bilayers, and molecular soft interfaces. 

Finally, using infrared-mediated heating, a noncontact method has been developed to accomplish rapid PCR amplification. With this method, near-infrared (IR) radiation is utilized to selectively heat the reaction solution through excitation of vibrational modes of water molecules By doing so,... 

Vibrational modes of water. [Used with permission from Marivi Fernandez-Serra.]... 

Figure 8.6 (a) A vibrational motion in a water molecule. The atoms are displaced, as shown by the arrows, and then reverse their directions to complete a cycle of vibration. (The vibration shown is one of three possible vibrational modes of water.) (b) A rotational motion of a water molecule about an axis through the oxygen atom. The molecule can also rotate with respect to the other two mutually perpendicular axes. 

The vibrational modes of water molecules are given in Figure 27a, where Vi and P2 are the symmetric modes and antisymmetric mode. 

FIGURE 27. Schematic diagrams of (a) the vibrational modes of water and (b) different configurations of adsorbed water molecules. 

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