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Vibration spectra materials

The vibrational spectrum of a metal complex is one of the most convenient and unambigious methods of characterization. However, it has not been possible to study the interactions of metal ions and biological polymers in this way since the number of vibrational bands from the polymer obscure the metal spectrum. The use of laser techniques for Raman spectroscopy now make it very likely that the Raman spectra of metals in the presence of large amounts of biological material will be measured (34). The intensity of Raman lines from metal-ligand vibrations can be... [Pg.30]

Despite the difficulty cited, the study of the vibrational spectrum of a liquid is useful to the extent that it is possible to separate intramolecular and inter-molecular modes of motion. It is now well established that the presence of disorder in a system can lead to localization of vibrational modes 28-34>, and that this localization is more pronounced the higher the vibrational frequency. It is also well established that there are low frequency coherent (phonon-like) excitations in a disordered material 35,36) These excitations are, however, heavily damped by virtue of the structural irregularities and the coupling between single molecule diffusive motion and collective motion of groups of atoms. [Pg.137]

Many of the studies of the vibrational spectrum of crystalline ice, prepared in thin films between cooled windows, have inadvertently dealt in part with the properties of H20(as). The most complete study, by Hardin and Harvey 48>, used samples prepared under conditions designed to yield material free of crystalline... [Pg.143]

In many applied areas, calculations can be used to screen a variety of materials to select materials with useful properties. In this case, if DFT calculations (or any other kind of theoretical method) can reliably predict that material A is significantly better than material B, C, D, or E for some numerical figure of merit, then they can be extremely useful. That is, the accuracy with which trends in a property among various materials can be predicted may be more important than the absolute numerical values of the property for a specific material. In other venues, however, the precision of a prediction for a specific property of a single material may be more important. If calculations are being used to aid in assigning the modes observed in the vibrational spectrum of a complex material, for example, it is important to understand whether the calculated results should be expected to lie within 0.01, 1, or 100 cm-1 of the true modes. [Pg.213]

Polyethylene has been studied spectroscopically in greater detail than any other polymer. This is primarily a result of its (supposedly) simple structure and the hope that its simple spectrum could be understood in detail. Yet as simple as this structure and spectrum are, a satisfactory analysis had not been made until relatively recently, and even then significant problems of interpretation still remained. The main reason for this is that this polymer in fact generally contains structures other than the simple planar zig-zag implied by (CH2CH2) there are not only impurities of various kinds that differ chemically from the above, but the polymer always contains some amorphous material. In the latter portion of the material the chain no longer assumes an extended planar zig-zag conformation, and as we have noted earlier, such ro-tationally isomeric forms of a molecule usually have different spectra. Furthermore, the molecule has a center of symmetry, which as we have seen implies that some modes will be infrared inactive but Raman active, so that until Raman spectra became available recently it was difficult to be certain of the interpretation of some aspects of the spectrum. As a result of this work, and of detailed studies on the spectra of n-paraffins, it now seems possible to present a quite detailed assignment of bands in the vibrational spectrum of polyethylene. [Pg.103]

Theoretical interpretation of molecular vibration spectra is not a simple task. It requires knowledge of symmetry and mathematical group theory to assign all the vibration bands in a spectrum precisely. For applications of vibrational spectroscopy to materials characterization, we can still interpret the vibrational spectra with relatively simple methods without extensive theoretical background knowledge. Here, we introduce some simple methods of vibrational spectrum interpretations. [Pg.290]

In sections 5.22 and 5.24, we have made schematic evaluations of the nature of the vibrational spectrum (see fig. 5.5). At this point, it is convenient to construct approximate model representations of the vibrational spectrum with the aim of gleaning some insight into how the vibrational free energy affects material properties such as the specific heat, the thermal expansion coefficient and processes such as structural phase transformations. One useful tool for characterizing a distribution such as the vibrational density of states is through its moments, defined by... [Pg.233]

H.G. Schimmel, M.R. Johnson, G.J. Kearley, A.J. Ramirez-Cuesta, J. Huot F.M. Mulder (2004). Materials Science and Engineering B-Solid State Materials for Advanced Technology, 108, 38-41. The vibrational spectrum of magnesium hydride from inelastic neutron scattering and density functional theory. [Pg.618]

X HE VIBRATIONAL SPECTRUM of any material consists of two parts the infrared (IR) and Raman spectra. IR spectroscopy is sensitive to the changes in dipole moment that occur during the vibrations of atoms that are forming chemical bonds. Raman spectroscopy detects the polarizability tensor changes of the electron clouds that surround these atoms. These apparent differences in the physical principles of both effects have led to the development of these two distinctly different techniques. IR and Raman spectra complement each other. Because they are sensitive to the vibrations of atoms, they are called vibrational spectra. [Pg.295]

Cotton et al. Already in their preliminary work, the authors explored the potentialities and goals of the SERRS technique for possible applications to bioanalytical problems. The first possibility is enhanced sensitivity for the RR scattering of scarce materials. A second possibility can be added specifically to redox-active chromophores in proteins. Indeed, this new spectroelectrochemical method permits the simultaneous study of an electrochemical reaction in a biological system in conjunction with a specific measurement of subtile variations in the vibrational spectrum of the chromophores. Another striking feature of the SERRS spectroscopy is that fluorescence of the adsorbate can be completely quenched by the metal surface which generates a high-quality Raman spectrum Another common application of SERRS spectroscopy is the study of the adsorption behaviour and conformation of biomolecules at the metal/electrolyte interface. [Pg.41]

Oiganometallic n-Complexes.—As explained (p. 88) only a selection of the material reported this year is presented. The vibrational spectrum of [(OQ4Cr-(bicyclo[2,2,l]heptadiene)] has been reported and the metal-olefin bond stretching mode was identified at ca. 250 cm" the lowest known frequency for such vibrations . A series of ten maleic anhydride complexes of the type (50) has been prepared by photochemical substitution reactions from the... [Pg.92]

Amorphous materials have no long-range crystalline order but since they maintain a molecular structure they still give a vibrational spectrum which may be distinct from the crystalline material. In comparison, the X-ray powder diffraction pattern of an amorphous material contains only a broad signal which yields no structural information. [Pg.222]

Another common method relies on the cluster approximation to study special sites in crystalline solids. This technique has been extensively employed to study acid catalyst sites in zeolites (e.g., Ba rtsch et al. 1994 Saer et al. 1999) and by Catlow and co-worker to study adsorption of organic molecules in zeolites (e.g.. Gale et al. 1993). In these types of studies, researchers are interested in particular vibrational modes observed in crystalline solids, so it is not necessary to compute the entire vibrational spectrum of a material. Hence, the cluster approximation is justified provided the cluster model is large enough to account for the solid environment surrounding the species of interest (see discussion above on gibbsite clusters). [Pg.475]


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Vibrational Spectra of Reference Materials

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