Far-IR region

According to Schroeder (1990) frequencies of the interlayer vibrational mode are 

Polarized measurements using single crystal flakes reveal no in-plane and out-ofplane dichroic character of bands at 110, 91 and 83 cm for muscovite, phlogopite and biotite, respectively, and proved the assignment to vibrations of the oxygen atoms that constitute the cage in which K is located (Laperche and Prost 1991). Weak pleochroic 

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Far-infrared (ir) spectroscopy, 23 142 Far-ir region, 74 234-236 Farm animals. See also Animal genetic engineering... 

In catalysis, infrared (IR) spectroscopy is commonly used to characterize specific adsorbates. Because of the localized nature and particular chemical specificity of molecular vibrations, IR spectra are quite rich in information, and can be used to extract or infer both structural and compositional information on the adsorbate itself as well as on its coordination on the surface of the catalyst. In some instances, IR spectroscopy is also suitable for the direct characterization of solids, especially if they can be probed in the far-IR region (10-200 cm ) [74-76],... 

Several methods are successfully applicable in this field, e.g. dielectric relaxation methods 164>, IR investigations in the near, fundamental, and far IR regions 165>, RAMAN spectroscopy 166>, NMR spectroscopy 32-34-16 ), and ultrasonic absorption i 8-i70). 

The metal-oxygen and related vibrations occur in the far IR region and these vibrations have been studied only in a few cases. In the complexes of lanthanide perchlorates with PyO, i>Ln o occurs in the region of 270-370 cm-1 (148). Three i n-o... 

Infrared (IR) radiation refers broadly to that part of the electromagnetic spectrum between the visible and microwave regions. Of greatest practical use to the organic chemist is the limited portion between 4000 and 400 cm-1. There has been some interest in the near-IR (14,290-4000 cm-1) and the far-IR regions, 700-200 cm-1. 

In the far IR region three markedly metal independent bands are observed, Le. out-of-plane vibration 340cm-1, Eu mode vibration 300cm-1 and metal-ligand vibration 150-200cm-1.198 The first two bands also exist in the H2(Pc) spectra with the second split into two. 

Pure rotational spectroscopy in the microwave or far IR regions joins electron diffraction as one of the two principal methods for the accurate determination of structural parameters of molecules in the gas phase. The relative merits of the two techniques should therefore be summarised. Microwave spectroscopy usually requires sample partial pressures some two orders of magnitude greater than those needed for electron diffraction, which limits its applicability where substances of low volatility are under scrutiny. Compared with electron diffraction, microwave spectra yield fewer experimental parameters more parameters can be obtained by resort to isotopic substitution, because the replacement of, say, 160 by lsO will affect the rotational constants (unless the O atom is at the centre of the molecule, where the rotational axes coincide) without significantly changing the structural parameters. The microwave spectrum of a very complex molecule of low symmetry may defy complete analysis. But the microwave lines are much sharper than the peaks in the radial distribution function obtained by electron diffraction, so that for a fairly simple molecule whose structure can be determined completely, microwave spectroscopy yields more accurate parameters. Thus internuclear distances can often be measured with uncertainties of the order of 0.001 pm, compared with (at best) 0.1 pm with electron diffraction. If the sample is a mixture of gaseous species (perhaps two or more isomers in equilibrium), it may be possible to unravel the lines due to the different components in the microwave spectrum, but such resolution is more difficult to accomplish with electron diffraction. 

Monodentate attachment to a metal ion lowers the symmetry of perchlorate to C3v and bidentate attachment to C2v (15-17). Consequently the number of vibrational modes should increase (Table I). In addition, a metal-oxygen stretching frequency would also be expected in the far-IR region and has been located in the range 360-290 cm-1 (18). These effects resulting on coordination, particularly the increase in the number of vibrational modes, may be used for identifying coordination of perchlorate. 

TO modes of a-Al203 [52] (Figure 3.7, lower part, where both the medium and the far IR regions are shown) correspond to the maxima at 636, 581, 439, 405 and 382cm and to the shoulder at 560cm . No fundamental TO modes are observed above 700 cm, in agreement with the six-coordination only for A1 in this structure. The bands at 871 and 490cm" are due to LO modes [53]. 

On the other hand, the Raman technique has been utilized in studying the important low frequency vibrations. Few IR studies extend below 250 cm because of the experimental difficulties of the far IR region,... 

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