Vibration modes, infrared spectroscop

The complexity of the physical properties of liquid water is largely determined by the presence of a three-dimensional hydrogen bond (HB) network [1]. The HB s undergo continuous transformations that occur on ultrafast timescales. The molecular vibrations are especially sensitive to the presence of the HB network. For example, the spectrum of the OH-stretch vibrational mode is substantially broadened and shifted towards lower frequencies if the OH-group is involved in the HB. Therefore, the microscopic structure and the dynamics of water are expected to manifest themselves in the IR vibrational spectrum, and, therefore, can be studied by methods of ultrafast infrared spectroscopy. It has been shown in a number of ultrafast spectroscopic experiments and computer simulations that dephasing dynamics of the OH-stretch vibrations of water molecules in the liquid phase occurs on sub-picosecond timescales [2-14],... 

Infrared and Raman are also rapid spectroscopic techniques that have been useful in the characterization of electrophiles in the condensed phase. Many superelectrophiles are expected to possess characteristic or new vibrational modes. The harmonic vibrational frequencies and infrared intensities for the nitronium ion (N02+) and protonitronium ion (HNO22"1") have been estimated using ab initio molecular orbital calculations (Table 5).37 Although the vibrational modes for the superelectrophile (HN022+) clearly differ from that of the monocation, data were so far not reported for the superelectrophile using infrared and Raman spectroscopy. When nitronium salts were dissolved in excess HF-SbFs, no apparent... 

Vibrational Spectroscopy [Infrared (mid-IR, NIR), Raman]. In contrast to X-ray powder diffraction, which probes the orderly arrangement of molecules in the crystal lattice, vibration spectroscopy probes differences in the influence of the solid state on the molecular spectroscopy. As a result, there is often a severe overlap of the majority of the spectra for different forms of the pharmaceutical. Sometimes complete resolution of the vibrational modes of a particular functional group suffices to differentiate the solid-state form and allows direct quantification. In other instances, particularly with near-infrared (NIR) spectroscopy, the overlap of spectral features results in the need to rely on more sophisticated approaches for quantification. Of the spectroscopic methods which have been shown to be useful for quantitative analysis, vibrational (mid-IR absorption, Raman scattering, and NIR) spectroscopy is perhaps the most amenable to routine, on-line, off-line, and quality-control quantitation. 

One of the main spectroscopic properties that differentiate fluoride glasses from silica-based glasses is the low multiphonon emission rate. These non-radiative relaxations that may strongly compete with radiative processes in rare-earth ions are nearly three orders of magnitude lower in ZBLAN glass than in silicate, as shown in Fig. 2. This property is directly related to the fundamental vibration modes of the host and, therefore, varies basically in the same manner as the infrared absorption edge. 

I 3 The Use of Infrared Spectroscopic Methods Table 3.2 Typical oxygen atom vibrational modes for metal oxide structures. 

Infrared and Raman spectroscopy are often grouped together, since both techniques provide information on the vibrational modes of a compound. However, since the two spectroscopic techniques are based on different physical principles the selection rules are different. Infrared spectroscopy is an absorption phenomenon, while the Raman spectroscopy is based on a scattering phenomenon (Raman and Krishnan 1928). In general, infrared energy is absorbed by polar groups, while radiation is more effectively scattered in the Raman effect by symmetric vibrations and nonpolar groups (Colthup et al. 1990 Ferraro and Nakamoto 1994). For most molecules other... 

Photons in the infrared region of the spectrum can be used to illuminate a particular substance, thus yielding, as with other spectroscopic techniques, information about the composition of the sample. A material with a certain composition will absorb certain frequencies of infrared radiation, converting the energy of the photons into vibrational modes in the electronic bonds. The absorption spectrum can be compared to that of known materials to determine the composition of the sample. 

In 1938 Marvel and co-workers started a series of papers under the title Hydrogen bonds involving the C-H link [49] (see also Ref. [50]). In parallel, infrared spectroscopic studies involving chloroform and bromoform were conducted in this period [51] revealing small red shifts of the j C H) stretching vibrational modes. The year of 1943 was marked by the first work by Huggins... 

A systematic infrared spectroscopic study of the mono acid triacylglycerols of the homologous fatty acids C2-C22 in solid state at —180 °C (and as liquids) for the different polymorphic forms was performed (De Ruig, 1971). The wagging, rocking-twisting and C-C stretching chain absorptions were co-ordinated with the well-established distributions of vibrational modes in hydrocarbon spectra. 

How is the pressure inside the DAC determined Usually, this is achieved by adding to the sample a small amount of a pressure calibrant with a known vibrational or electronic spectroscopic response to changes in pressure. For the infrared, a material such as powdered NaNOs is normally used—the symmetric N—O stretching mode of the NOs group is located at 1,401.3 cm at ambient pressure and moves steadily to higher wavenumbers with increasing pressure. For the Raman, the most common pressure calibrant is a ruby chip—the Ri fluorescence of ruby at 694.2 nm has a well-established pressure dependence up to 160kbar. More recently, it has been shown that the t2g phonon mode of the diamonds in the DAC itself, located at 1,332.5 cm at ambient pressure, can be used as an in situ calibrant for pressures up to 50 kbar. ... 

An alternative approach to the dynamics of a protein or one of its constituent elements (e.g., an a-helix) is to assume that the harmonic approximation is valid. Early attempts to examine dynamical properties of proteins or their fragments used the harmonic approximation. They were motivated by vibrational spectroscopic studies [24], where the calculation of normal mode frequencies from empirical potential functions has long been a standard step in the assignment of infrared spectra [25]. In calculating the normal vibrational modes of a molecule, one assumes that the vibrational displacements of the atoms from their equilibrium positions are... 

Vibrational spectroscopy is the collective term used to describe anal3 tical methods based on photons that induce transitions between vibrational states in molecules. Infrared (IR) and Raman spectroscopy are the two most commonly used types of vibrational spectroscopy in polymer analysis. Both spectroscopic methods provide detailed information on the molecular-level about the structure, conformation and constitution of polymers. IR and Raman spectroscopy are considered as complementary methods. Many, but not all, vibrational modes are IR as well as Raman active. Generally, a molecular vibration is IR active only if it results in a change in the dipole moment of the molecule. In contrast to IR, a molecular vibration is Raman active only if it results in a change in the polarizability of the molecule. [92Gar]... 

Syndiotactic polypropylene also exists as two crystalline modifications, the more stable one possessing a helical conformation and the other a planar zig-zag, A detailed analysis of the Raman spectrum confirms these structures and there is an excellent correlation between observed and predicted vibrational modes of the helical structure. Painter et al. have made a Fourier transform infrared spectroscopic study of isotactic polypropylene in the crystalline and amorphous state. The spectrum of the amorphous regions is broadly similar to that of the melt, but there is evidence for short sequences of helical segments in the amorphous phase, while the crystalline phase has longer sequences. This puts a different interpretation on the distinction between amorphous and crystalline regions than previously considered. 

In the same year, our group in Lausanne published first results from a similar instrument which was equipped with an electrospray ion source for producing closed-shell biomolecular ions, the first demonstrations of which were the measurement of the UV spectra of cold, protmiated aromatic amino acids, tryptophan [46], tyrosine [46, 122], and phenylalanine [122]. Spectroscopic detection is achieved by measuring the small percentage of parent ions that fragment subsequent to UV absorption. The internal temperature of the ions was estimated to be 11-16 K from an analysis of the intensity of hot band transitions of low frequency vibrational modes. If the temperatures achieved in buffer-gas cooled ion traps are low enough and the spectra sufficiently simple, one can often resolve UV absorption spectra for different stable cOTiformers of the molecule [122]. In this case, one can use the IR-UV double resonance techniques so profitably employed in supersonic molecular beam studies [91,123-128] to measure conformer-specific infrared spectra, and this was applied by Steams et al. to both individual amino acids [129] as well as peptides with up to 12 amino acid residues [130]. Subsequent improvements to the Lausanne machine (Fig. 7) included the addition of an ion funnel to... 

Phase separation and spatial organization of membrane domains determine the state of water, fundamental interactions in the polymer/water/ion system, vibration modes of fixed sulfonate groups, and mobilities of water molecules and protons. Dynamic properties of the membrane can be probed at the microscopic scale with spectroscopic techniques, including Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) (Mauritz and Moore, 2004). FTIR... 

Hellwig P, Grzybek S, Behr J, Ludwig B, Michel H, Mntele W. Electrochemical and ultraviolet/visible/infrared spectroscopic analysis of hemea and redox reactions in the C3dochrome c oxidase from Paracoccus denitrificans separation of heme a and a contributions and assignment of vibrational modes. Biochemistry 1999 38 1685-1694. 

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