Interpretation of vibrational

A series of monographs and correlation tables exist for the interpretation of vibrational spectra [52-55]. However, the relationship of frequency characteristics and structural features is rather complicated and the number of known correlations between IR spectra and structures is very large. In many cases, it is almost impossible to analyze a molecular structure without the aid of computational techniques. Existing approaches are mainly based on the interpretation of vibrational spectra by mathematical models, rule sets, and decision trees or fuzzy logic approaches. 

Vibrational spectroscopy has played a very important role in the development of potential functions for molecular mechanics studies of proteins. Force constants which appear in the energy expressions are heavily parameterized from infrared and Raman studies of small model compounds. One approach to the interpretation of vibrational spectra for biopolymers has been a harmonic analysis whereby spectra are fit by geometry and/or force constant changes. There are a number of reasons for developing other approaches. The consistent force field (CFF) type potentials used in computer simulations are meant to model the motions of the atoms over a large ranee of conformations and, implicitly temperatures, without reparameterization. It is also desirable to develop a formalism for interpreting vibrational spectra which takes into account the variation in the conformations of the chromophore and surroundings which occur due to thermal motions. 

For isolated molecules a variety of approaches have proved useful in the interpretation of vibrational spectra. Firstly, a species may approximate to a symmetry higher than its actual. In such cases a correlation with-descent in symmetry from — the higher symmetry usually simplifies the interpretation of its spectra. Secondly, local group vibrations, essentially uncoupled from the vibration of other equivalent or near-equivalent groups, may occur. Thirdly, chemically distinct groups may couple... 

We have seen in section 3.1 the application of the concept of the harmonic oscillator in the interpretation of vibrational properties of crystals. For a unidimensional harmonic oscillator, there is a single degree of freedom ... 

The interpretation of vibrational and electronic spectra of these complexes is much more complicated. Whereas IR spectra generally show only bands of low intensity, tbe Raman spectra often display intense and characteristic lines. Rigorous assignments have not been published so far, but the most simple M(/i2-S), ring systems can easily be... 

Figure 1.2. Plan view of the Ni(lll)c(4 x 2)-CO surface phase showing the bridge site model favoured for many years on the basis of the interpretation of vibrational spectroscopy, and the mixed-hollow site model subsequently established through SEXAFS, PhD, and LEED measurements. To allow visibility of all surface atoms the C atoms are shown as the larger dark-shaded spheres and the atoms as smaller white spheres. The full lines show the primitive unit mesh while the dashed lines show the centred (4 x 2) unit mesh.

IV. Considerations Relating to the Interpretation of Vibrational Spectra of Adsorbed Species... 

The interpretation of vibrational spectra is dependent on a correct assessment of the symmetry properties of the adsorbed species themselves and of their vibrational modes. Several general accounts have been given of the classification of vibrations of adsorbed species in terms of the symmetry elements associated with a surface complex (89, 90). 

Interpretation of vibrational spectra of C60H2n is difficult because of uncertainty in the isomeric composition of the samples, presence of impurities, and low intensity of many absorption bands. The IR spectra of C60H2, presumably a product of 1,2-addition to the 6-6 bond was reported in (Ballenweg et al. 1993). The IR spectrum of C60H6 considered as a mixture of the C3 and D3 isomers was presented by Bergosh et al. (1997). The IR and Raman spectra of C60H36 and C60Hlg were studied... 

INTERPRETATION OF VIBRATIONAL SPECTRA IN ELECTROCHEMICAL ENVIRONMENTS FROM FIRST-PRINCIPLE CALCULATIONS COMPUTATIONAL STRATEGIES... 

Interpretation of vibrational spectra in electrochemical environments from first-principle calculations computational strategies 211... 

While there are many indications that oxygen coordinated solvation of cations in NMA is predominant, there have been suggestions that nitrogen coordination solvation of cations also may occur216,217). Much of the evidence for this is based on the interpretation of vibrational spectral data for solid solvates and these data have shown a remarkable flexibility toward interpretation217 218). It is quite possible that the type of coordination may depend strongly on the particular ion involved. 

Kubicki, J.D., Interpretation of vibrational spectra using molecular orbital theory calculations, in Molecular Modeling Theory Applications in the Geosciences, Cygan, R.T. and Kubicki, J.D., Eds., Geochemical Society of America, Washington, D.C., 2001, p. 459. 

In this section, we shall compare briefly the approach to molecular spectra using the Hamiltonian described in this paper with the standard approach Such a comparison is useful because it shows future trends and problems in the theoretical interpretation of vibration-rotation spectra of molecules. 

Qualitative analysis of unknown compounds. Interpretation of vibrational spectra with the help of empirical rules... 

Vibrational spectra of solid carbonyls often differ from those in solution. The latter often exhibit very complicated spectra, since many isomers exist in an equilibrium. Even the interpretation of vibrational spectra of the species Fe3(CO)i2, whose size is small compared to many of the large carbonyl clusters which have been investigated during the past few years, is controversial (Cotton and Hunter, 1974). 

A further problem in the interpretation of vibrational spectra of solid state compounds arises from the different phases of the vibrations in neighboring cells, leading to a wave described by the wave vector k. In the absence of a phase difference, k equals zero. This is the basis for the factor group analysis. If the vibrational motions are oriented parallel to the direction of the wave caused by the phase differences, a longitudinal branch results while transverse branches result from orthogonal vibrational motions. Furthermore, it is necessary to differentiate between optical and acoustic modes. In the optical mode of the NaCl lattice, Na+ and Cl ions have opposite displacements, while the acoustic modes are caused by in-phase motions of Na+ and CF. 

M. Diem, Introduction to Modem Vibrational Spectroscopy , John Wiley Sons, New York, 1993. This easy to read book features detailed discussion of the theoretical and experimental aspects of IR and Raman spectroscopy and provides many examples for the interpretation of vibrational spectra. 

Luinge, H.J. Automated interpretation of vibrational spectra. Vibr. Spectrosc. 1990, 1, 3-18. 

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