Infrared and Raman Bands

Breuillard C., Ouillon R. Infrared and Raman band shapes and dynamics of molecular motions for N20 in solutions v3 band in CCL and liquid SF6. Mol. Phys. 33, 747-57 (1977). 

On the basis of these assignments, the two bands must be associated with the presence of isolated Ti atoms in tetrahedral coordination within the silicalite framework. Consequently, a quantitative linear correlation between the Ti02 content and the intensities of both the infrared and Raman bands at 960 cm-1 is expected—and this is indeed observed, as shown in Fig. 9b. 

Infrared and Raman Band at 960 cm-1 assigned to Ti-O-Si vibration (Caution Si-OH and defect sites in silicalites also show this feature). 

The most recent fairly comprehensive review Of the vibrational spectra of transition metal carbonyls is contained in the book by Braterman1. This provides a literature coverage up to the end of 1971 and so the subject of the present article is the literature from 1972 through to the end of 1975. Inevitably, some considerable selectivity has been necessary. For instance, a considerable number of largely preparative papers are not included in the present article. Tables A-E provide a general view of the work reported in the period. Table A covers spectral reports and papers for which topics related purely to vibrational analysis are not the main objective. Papers with the latter more in view are covered in Table C. Evidently, the division between the two is somewhat arbitrary. Other tables are devoted to papers primarily concerned with the spectra of crystalline samples — Table B — to reports of infrared and Raman band intensities — Table D and sundry experimental techniques or observations - Table E. Papers on matrix isolated species, which are covered elsewhere in this volume, are excluded. 

Table la. Infrared and Raman Band Assignments for EPON 828 17)... 

Before discussing other examples, we note here that, for a centrosymmet-ric molecule (one with an inversion center), rx, ry, and rz are u (from the German word ungerade, meaning odd) species, while binary products of x, y, and z have g (gerade, meaning even) symmetry. Thus infrared active modes will be Raman forbidden, and Raman active modes will be infrared forbidden. In other words, there are no coincident infrared and Raman bands for a centrosymmetric molecule. This relationship is known as the mle of mutual exclusion. 

Carbon dioxide, C02, is a fairly small molecule with acidic properties, which has frequently been used as a probe molecule for basic surface sites and as a poison in catalytic reactions. As shown in the following, C02 adsorption onto oxide surfaces leads to a variety of surface species such as bicarbonates and carbonates that coordinate to surface metal ions in various ways. The type of the coordination influences the symmetry of these ligands so that different surface species held by distinct surface sites can be distinguished by means of their infrared absorptions (162). The characteristic infrared (and Raman) bands of C02 and possible surface species are summarized in Table VI. The wave-number range below 1000 cm"1 was usually not accessible in studies on adsorbed C02 because of the strong absorption of the oxides at lower wave numbers. 

Infrared (and Raman) Bands and Assignments of CO2 and Carbonate Species... 

Fig. 29. (a) Calculated frequencies in the amide I region for the 10 lowest energy conformations of cyclo(L-Ala—Gly-Aca) (see Table XXVII). The observed infrared (solid bar) and Raman (open bar) bands are shown on the bottom line. Numbers above the computed frequencies represent the groups involved in the vibration (Maxfield et al., 1981). (b) Calculated frequencies in the amide V region for the 10 lowest energy conformations of cyclo(i.-Ala—Gly-Aca) (see Table XXVII). The observed infrared and Raman bands occur at the same frequencies and are indicated by the shaded bars on the bottom line. Numbers above the calculated frequencies represent the groups involved in the vibration (Maxfield et al., 1981). 

The defect formation can be studied by measuring the characteristic infrared and Raman bands. Fig. 4.6 shows, for instance, the variation of the 476cm HS04 bending band its intensity (and frequency) decreases with increasing temperature and changes suddenly at the I -> II transition at 318 K. The intensity of this band, however, does not reach zero at the I - II transition but only at the subsequent II - III... 

Information about phase transitions can be obtained by studying the frequency, intensity and width of infrared and Raman bands as a function of temperature and pressure. The low-frequency bands associated with... 

From Table 3.5 we also observe that it is possible to calculate the intensities of infrared and Raman bands, but in order for this process to generate accurate results we need to employ large, diffuse basis sets. This is because computation of dipole moments and polarizability derivatives require that the tail of the electron density region be properly modeled. Specialized basis sets have been developed for this purpose, and a comparison of their performance can be found in [20]. 

Determine the point groups and the numbers of infrared and Raman bands that would be expeeted for the cis and trans isomers of SCI2F4. 

Levi G, Marsault JP, Marsaultherail F, McClung RED (1980) The Fokker-Planck-Langevin model for rotational Brownian-motion. 2. Comparison with the extended rotational diffusion-model and with observed infrared and Raman band shapes of linear and spherical molecules in fluids. J Chem Phys 73(5) 2443-2453... 

Fig. 3 also shows that the polyethylene crystal has two infrared active lattice vibrations. The frequency calculated for the infrared active Vs(n) vibration is 76 cm" in agreement with the observed 72.5 cm" The dichroism [14] and the isotope shift [15] confirm this assignment. The fact that this band is not observed for the triclinic crystal [15] also supports the assignment, since its primitive unit cell has only one chain. Although there are many points to be improved, the infrared and Raman bands are reasonably interpretated by the normal coordinate treatments. 

The small step rotational diffusion model has been extensively applied to interpret ESR linewidth [7.4, 7.9], dielectric relaxation [7.2], fluorescence depolarization [7.19], infrared and Raman band shapes [7.24], as well as NMR relaxation in liquid crystals [7.14, 7.25]. When dealing with internal rotations in flexible mesogens, they are often assumed to be uncoupled from reorientation to give the so-called superimposed rotations model. Either the strong collision model or the small step rotational diffusion model may be used to describe [7.26, 7.27] molecular reorientation. 

Fundamental Molecular Vibrations Mid-infrared and Raman Bands... 

This correlation ubie predicts that the molecular vibrations of TXntS chain will split into two due 10 the inteimoiccular interactkms one is infrared active and the other is Raman active. Therefore we may not expect any band splitting in the infrared spectra as well as in the Raman spectra, but mutual exclusion should be observed as a slight band gap between the frequencies of the infrared and Raman bands. On the other hand, if the space group is P2,-Cj or Pl-C then all the intramolecular vibrations should be split into two bands due to the coupling effect of a symmetry reduction in the molecular chain at a site (site symmetry Cl) and inteimoiccular correlation of the adjacent two chains. The correlation table should become as follows. 

A dose view of the infrared and Raman spectra measured at room temperature (Figure 18) and at liquid nitrogen temperature does not give any delectable amount of band splitting in eadi spectrum, inconsistent whb the above-mentioned prediction for space group P2 or PI. On the other hand, according to the lattice vibrational calculation made for die structural model of P2 /c. the frequency gap between the infrared and Raman bands of the oarresponding vibrational mote is too small. 2-3 cm at moat, to detect in the observed spectral data beyond the experimental error. Therefore it may be difficult... 

AMBER A Program for Simulation of Biological and Organic Molecules Atoms in Molecules CHARMM The Energy Function and Its Parameterization Force Fields A Brief Introduction Force Fields A General Discussion Force Fields CFF GROMOS Force Field Intensities of Infrared and Raman Bands OPLS Force Fields,... 

The definition of here differs by a factor of i/2n from that introduced by Stephens. The rotatory strengths of the fundamental vibrational transitions are thus determined by the APT, AAT, and the molecular force field from which the descriptions of the yibrational normal modes are derived. The evaluation ot the force field and APTs, which determine the infrared (IR) intensities (see Intensities of Infrared and Raman Bands), has been well established both at the SCF and higher levels of theory, for instance second-order Mpller-Plesset (MP2) theory, and used in the evaluation of VCD intensities. The calculation... 

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