Infrared and Raman spectroscopies

The IR and Raman spectra of organosilicon compounds have been thoroughly studied and largely systematised. Shifts in the valence vibrations (symmetrical) and Vas (asymmetrical) yield essential information. If one or two methyl groups in tetramethylsilane (Vj = 598 cm , = 696 cm ) are replaced by carbofunctional 

If groups with sp (olefins) or sp (alkynes, CN) hybridisation are bonded to the trimethylsilyl kernel, the value of is greatly decreased. This effect is reinforced extraordinarily if an extended ethyne group is loaded with heavy atoms, such as bromine or iodine. In these cases drops to the values of 372 and 366cm , respectively. [635]. Table 5.1 shows the and values for various tetramethylsilane derivatives. 

The deformation vibrations S of the Si—C bonds occur at both higher and lower wave numbers than valence vibrations. A strong 5(Si—C) band at 1265-1250 cm is characteristic of alkylsilanes [643], while arlysilanes are characterised by 5 (Si—C) bands at 1430 and 1100 cm [644- 646]. 

A Low molecular weight branched polymer. B Linear polymer, moderate phenyl content. C Linear polymer, large phenyl content. 

6 INFRARED AND RAMAN SPECTROSCOPY ° ° 21-138 Applications The following use was made of infrared and Raman spectroscopy identification of surface groups on treated and untreated fumed silica, tion of silica functional groups and coatings by Raman spectroscopy. 

Testing procedure In general, standard methods were used, with some improvements to obtain better resolution. A photoacoustic detector was used to obtain spectra of fumed silica. A carbon black background was used. In studies of adhesion of coatings on metal substrates, a gold coated background was used as the reference. 4 Diffuse respectra, and kaolin. 2 A 

were used to characterize surface species on alumina 2  

Raman microprobe was capable of obtaining spectra from a very small area (2 pm 

Two peaks on the IR spectrum (1720 and 1580 cm ) have a linear correlation with 135 

Closely related to IR spectroscopy is a technique called Raman spectroscopy. As radiation passes through a transparent medium, a small proportion of the incident beam is scattered in all directions. Most of the incident radiation is 

IR and Raman spectroscopies are very important tools for characterization of the chemical and physical nature of polymers. Due to the high sensitivity of IR spectroscopy to changes in the dipole moment of a given vibrating group, this technique is intensively used to identify polar groups. In contrast, Raman spectroscopy is especially helpful in the characterization of the homonuclear polymer backbone due 

Vibrational spectra have been used to identify matrix-isolated chalcogen-nitrogen species, which are unstable under ambient conditions.In this way the species NS, SNS (and the less stable isomer NSS), NNS, NSe, SeNSe and [SeNSe] have been identified. The technique of N-enrichment has been used in several cases to distinguish S-N from S-S vibrations. 

Raman spectroscopy is a useful probe for detecting transannular S - S interactions in bicyclic or cage S-N molecules or ions. The strongly Raman active vibrations occur at frequencies in the range 180-300 cm and for S- S distances in the range 2.4-2.7 A. On the basis of symmetry considerations, the Raman spectrum of the mixed sulfur-selenium nitride S2Sc2N4 was assigned to the 1,5- rather than the 1,3- isomer.  

The explosive and insoluble black solid Se3N2Cl2 was shown to contain the five-membered cyclic cation [Se3N2Cl] by comparing the calculated fundamental vibrations with the experimental IR spectrum. 

The technique of N-enrichment has been used in several cases to distinguish S-N from S-S vibrations. The IR and Raman spectra of 

In cases where information about atomic arrangements cannot be obtained by X-ray crystallography owing to the insolubility or instability of a compound, vibrational spectroscopy may provide valuable insights. For example, the explosive and insoluble black solid SesNaCla was shown to contain the five-membered cyclic cation [SesNaCl] by comparing the calculated fundamental vibrations with the experimental IR spectrum.  

It has already been illustrated in the previous chapters that Raman spectroscopy suits outstandingly well to characterizing different types of carbon materials. In particular, the fact of sp - and sp -carbon showing clearly distinguishable signals renders the Raman technique a powerful tool for determining the phase purity as well as other structural features both in bulk phase or in grain boundaries. 

The characterization of ultrananocrystalline diamond with its large portion of grain boundaries benefits as well from the application of Raman spectroscopy as the content of sp -material in a sample can be determined rather exactly this way. In addition to the aforementioned dependency on the excitation wavelength, the 

Vibrational spectroscopy of organoselenium compounds is a relatively young area and most reports have been published since approximately Raman, instead of 

As expected, when comparing vibrational spectra of sulfur and selenium compounds, the absorptions due to bonds to selenium occur at lower frequencies than the corresponding sulfur modes. This frequency shift is normally 50-150 cm but may be more for selenium-oxygen compounds when compared to sulfur-oxygen compounds  

Selenols are of particular interest with regard to biochemical selenium compounds and the Se-H stretch normally appears from 2280-2330 cm . This band is not influenced significantly by concentration effects, solvent effects or the state of aggregation, demonstrating that, as expected, selenols have very little tendency to form inter-molecular hydrogen bonds  

Finally, vibrational absorption bands of selenium-oxygen compounds might be of interest in the study of selenium in biological systems and the basic classes of Se-0 molecules have been exhaustively studied Relevant bands are 1010-1040 cm (vjs (O-Se-0) in selenates), 930-960 cm (v, (O-Se-0) in selenates), 930 cm (v (Se=0) in selenites), 850-900 cm (v (Se=0) in selenenic acids, esters and anhydrides), 800-840 cm (v (Se=0) in selenoxides) and 680-700 cm (v (Se-OH) in selenenic acids)  

At this time it would appear prudent for a vibrational spectroscopist to undertake a careful and detailed experimental vibrational study of solutions of selenocysteine under various conditions since selenocysteine residues seem to occur in most, if not all, naturally occurring selenoproteins. The facile oxidation of this selenoamino acid must be kept in mind and any vibrational study must be carried out under carefully controlled conditions. 

Since vibrational frequencies depend on the masses of moving atoms, the substitution of an atom in a molecule by an isotope of different mass will alter the frequencies of those modes in which the substituted atom moves significantly. This technique may be useful in distinguishing between two possibilities for the assignment of a vibrational band. For example, the vibrational 

For a more detailed discussion of the theoretical aspects of infrared and Raman spectroscopy, and additional applications of this technique to inorganic ring systems, the reader is referred to the book by Nakamoto.  

Fourier-transform infrared (FTIR) spectroscopy is an invaluable characterization technique used to confirm the chemical structure of a polymer, particularly through the observation of vibrational transitions associated with specific functional groups [185,186]. The technique has been extensively used for the characterization of polymer blends and several reviews have appeared in the literature [187-190]. FTIR measurements can help identify the mechanism of interaction between the components of a polymer blend. For example, FTIR studies carried out by Hsu and coworkers [191] have shown that the favorable interaction between PS and PVME can be monitored through the C—H out-of-plane vibration of the phenyl ring at 698 cm in PS and the COCH3 vibration of PVME (doublet at 1085 and 1107 cm ). Changes in the position and intensity of the IR bands can be used to monitor changes in miscibility behavior ]192, 193]. 

Coleman and Painter have reported that the miscibility in hydrogen bonded blends is primarily dictated by the balance between unfavorable physical and favorable chemical interactions [187,190]. They have developed a model, called the association model, that makes use of the self- and inter-association equilibrium constants 

Studies similar to those described above can be carried out on polyamides [207] and polyurethanes [208, 209]. Moreover, infrared spectroscopy has been used to study intermolecular interactions in amorphous /crystalline binary blends such as mixtures of poly(caprolactone) [210] or (polyethylene oxide) [211] and poly(vinylphenol). 

A more recent development in this area is FTIR imaging. This technique is a powerful tool that can be used to study a range of polymer systems, including multilayer polymer films, composite materials, fibers, and blends [212]. By selecting the characteristic bands of a chemical species, its spatial distribution can be mapped. Conventional infrared microspectroscopy uses apertures to limit the examined area 

The determination of polymer-polymer miscibility is a very important aspect of blending. In this chapter we have reviewed the main techniques now in use for the assessment of blend miscibility. Owing to the delicate balance between entropic and enthalpic terms as well as the large size of polymer molecules, miscibility is often difficult to assess. In some cases this difficulty has led to apparently contradictory results being reported in the literature. For this reason, whenever possible, multiple experimental probes should be used to unequivocally assess if a blend is miscible. 

A comprehensive historical review of the analytical applications of infrared spectroscopy from the first experiments to the introduction of FTIR spectrometers has appeared.221 The first study of the absorption of infrared radiation by a range of chemical substances was made in 1881 by Abney and Festing, after the former had developed a photographic method of detecting radiation in the near-infrared region. Over the next 25 years a number of other studies were made. This early phase culminated in the work of W. W. Coblentz in the United States, which was published in 1905.222 It became evident from Coblentz s data that infrared spectra were related to molecular structure, but IR spectroscopy remained principally the province of researchers in university physics departments until World War n. 

Chemists only began to use the technique routinely when commercial IR spectrometers had been developed.223 226 Three wartime research programmes created the initial demand, and provided the impetus for the production of commercial instruments. These were the US synthetic rubber programme,227 the British project to identify hydrocarbons in fuels from enemy aircraft,228 and the joint British-US penicillin programme. The mineral oil mull technique for obtaining the IR spectrum 

Since IR spectroscopy is a standard, and perhaps currently the most widely used tool in the search for and characterization of polymorphs, there are likely to be thousands of references to the use of the technique in connection with polymorphs. The vast majority of these deal with the determination of the IR fingerprint of a polymorphic modification. In this section, we wish to note a few cases in which the IR and Raman techniques were employed to obtain chemical information somewhat beyond the mere identification of a particular crystal modification. For instance, Mathieu (1973) showed for a number of chiral compounds that it is possible to distinguish between a dl racemate and a conglomerate of d and / crystals by use of IR and/or Raman spectroscopy, even when it may not be possible to make such a distinction by physical or visual means. 

As in many studies of polymorphism the combination of techniques is particularly effective for obtaining structure-property relationships (Yu et al. 1998). Combining IR with SSNMR and X-ray crystallography to study the two polymorphs of 6-XXXIII, Fletton et al. (1986) were able to correlate the IR frequencies with the number of molecules in the unit cell as well as the intramolecular and intermolecular hydrogen bonding. 

Most interactions of electromagnetic radiation with matter contain a geometric, as well as an energetic component. For visible and ultraviolet absorption this is because the fundamental relationship governing the absorption of light is the transition moment integral, (6.1), in which r is the transition moment vector defining 

The utility of such an approach is demonstrated on the molecular level with the case of benzylideneaniline 6-XXXV (R-H), which occupied spectroscopists for nearly three decades (Haselbach and Heilbronner 1968, and references therein). This material is isoelectronic with azobenzene 6-XXXVI and stilbene 6-XXXVII, but its solution absorption spectrum differs significantly from them (Fig. 6.18). 

The existence of two polymorphic structures of the dichloro derivative of 6-XXXV (R = Cl) (Bernstein and Izak 1976) provided an opportunity for the direct examination of the relationship between the molecular structure and the electronic spectrum. The two structures are conformational polymorphs, with the metastable very pale yellow triclinic needle form exhibiting a planar molecular conformation a = fi = 0°) (Bernstein and Schmidt 1972) and the stable yellow orthorhombic form (with chunky rhombic crystals) exhibiting a non-planar conformation (a = 25° fi = —25°) (Bernstein and Izak 1976). Assuming that the two crystal structures merely serve to hold the molecule in the two different conformations (i.e. the oriented gas model), the absorption spectra should reflect the difference in conformation that measured on the triclinic structure, with a planar conformation, should closely resemble the spectra of 6-XXXVI and 6-XXXVII, while that for the orthorhombic structure, with the nonplanar molecular conformation, should retain the characteristics of 6-XXXV (R = H) in solution. 

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Infrared and Raman spectroscopy each probe vibrational motion, but respond to a different manifestation of it. Infrared spectroscopy is sensitive to a change in the dipole moment as a function of the vibrational motion, whereas Raman spectroscopy probes the change in polarizability as the molecule undergoes vibrations. Resonance Raman spectroscopy also couples to excited electronic states, and can yield fiirtlier infomiation regarding the identity of the vibration. Raman and IR spectroscopy are often complementary, both in the type of systems tliat can be studied, as well as the infomiation obtained. 

Both infrared and Raman spectroscopy provide infonnation on the vibrational motion of molecules. The teclmiques employed differ, but the underlying molecular motion is the same. A qualitative description of IR and Raman spectroscopies is first presented. Then a slightly more rigorous development will be described. For both IR and Raman spectroscopy, the fiindamental interaction is between a dipole moment and an electromagnetic field. Ultimately, the two... 

Advances in Infrared and Raman Spectroscopy [36] provides review articles, both fiindamental and applied, in the fields... 

Lee D and Albrecht A C 1985 A unified view of Raman, resonance Raman, and fluorescence spectroscopy (and their analogues in two-photon absorption) Advances in Infrared and Raman Spectroscopy vo 12, ed R J H Clark and R E Hester (New York Wiley) pp 179-213... 

Bewiok A and Pons S 1985 Infrared speotrosoopy of the eleotrode-eleetrolyte solution interfaoe Advances in Infrared and Raman Spectroscopy ed R J FI Clark and R E Flester (New York Wiley Fleyden) 12 1-63... 

This book, originally published in 1950, is the first of a classic tliree-volume set on molecular spectroscopy. A rather complete discussion of diatomic electronic spectroscopy is presented. Volumes 11 (1945) and 111 (1967) discuss infrared and Raman spectroscopy and polyatomic electronic spectroscopy, respectively. 

The vibrational states of a molecule are observed experimentally via infrared and Raman spectroscopy. These techniques can help to determine molecular structure and environment. In order to gain such useful information, it is necessary to determine what vibrational motion corresponds to each peak in the spectrum. This assignment can be quite difficult due to the large number of closely spaced peaks possible even in fairly simple molecules. In order to aid in this assignment, many workers use computer simulations to calculate the vibrational frequencies of molecules. This chapter presents a brief description of the various computational techniques available. 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

Equations (6.5) and (6.12) contain terms in x to the second and higher powers. If the expressions for the dipole moment /i and the polarizability a were linear in x, then /i and ot would be said to vary harmonically with x. The effect of higher terms is known as anharmonicity and, because this particular kind of anharmonicity is concerned with electrical properties of a molecule, it is referred to as electrical anharmonicity. One effect of it is to cause the vibrational selection mle Au = 1 in infrared and Raman spectroscopy to be modified to Au = 1, 2, 3,. However, since electrical anharmonicity is usually small, the effect is to make only a very small contribution to the intensities of Av = 2, 3,. .. transitions, which are known as vibrational overtones. 

Schrader, B. (1995) Infrared and Raman Spectroscopy, Wiley-VCH, Weinheim. 

A small but artistically interesting use of fluorspar is ia the productioa of vases, cups, and other ornamental objects popularly known as Blue John, after the Blue John Mine, Derbyshire, U.K. Optical quaUty fluorite, sometimes from natural crystals, but more often artificially grown, is important ia use as iafrared transmission wiadows and leases (70) and optical components of high energy laser systems (see Infrared and RAMAN spectroscopy Lasers) (71). 

Materials characterization techniques, ie, atomic and molecular identification and analysis, ate discussed ia articles the tides of which, for the most part, are descriptive of the analytical method. For example, both iaftared (it) and near iaftared analysis (nira) are described ia Infrared and raman SPECTROSCOPY. Nucleai magaetic resoaance (nmr) and electron spia resonance (esr) are discussed ia Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed ia Spectroscopy (see also Chemiluminescence Electho-analytical techniques It unoassay Mass specthot thy Microscopy Microwave technology Plasma technology and X-ray technology). 

Instrumental Interface. Gc/fdr instmmentation has developed around two different types of interfacing. The most common is the on-the-fly or flow cell interface in which gc effluent is dkected into a gold-coated cell or light pipe where the sample is subjected to infrared radiation (see Infrared and raman spectroscopy). Infrared transparent windows, usually made of potassium bromide, are fastened to the ends of the flow cell and the radiation is then dkected to a detector having a very fast response-time. In this light pipe type of interface, infrared spectra are generated by ratioing reference scans obtained when only carrier gas is in the cell to sample scans when a gc peak appears. 

Reaction with hydrogen is very slight below 800°C, but reduction occurs at higher temperatures. In addition to some SiO formation, the formation of SiOH and SiH groups has been demonstrated by infrared and Raman spectroscopy (96). 

B. Schrader, Infrared and Raman Spectroscopy Methods and Applications, VCH Pubhshers, New York, 1994. 

Infrared (ir) transmission depends on the vibrational characteristics of the atoms rather than the electrons (see Infrared and Raman spectroscopy). For a diatomic harmonic oscillator, the vibrational frequency is described by... 

Infrared (in) spectrometers are gaining popularity as detectors for gas chromatographic systems, particularly because the Fourier transform iafrared (ftir) spectrometer allows spectra of the eluting stream to be gathered quickly. Gc/k data are valuable alone and as an adjunct to gc/ms experiments. Gc/k is a definitive tool for identification of isomers (see Infrared and raman spectroscopy). 

Infrared Spectrophotometry. The isotope effect on the vibrational spectmm of D2O makes infrared spectrophotometry the method of choice for deuterium analysis. It is as rapid as mass spectrometry, does not suffer from memory effects, and requites less expensive laboratory equipment. Measurement at either the O—H fundamental vibration at 2.94 p.m (O—H) or 3.82 p.m (O—D) can be used. This method is equally appticable to low concentrations of D2O in H2O, or the reverse (86,87). Absorption in the near infrared can also be used (88,89) and this procedure is particularly useful (see Infrared and raman spectroscopy Spectroscopy). The D/H ratio in the nonexchangeable positions in organic compounds can be determined by a combination of exchange and spectrophotometric methods (90). 

Normal mode analysis exists as one of the two main simulation techniques used to probe the large-scale internal dynamics of biological molecules. It has a direct connection to the experimental techniques of infrared and Raman spectroscopy, and the process of comparing these experimental results with the results of normal mode analysis continues. However, these experimental techniques are not yet able to access directly the lowest frequency modes of motion that are thought to relate to the functional motions in proteins or other large biological molecules. It is these modes, with frequencies of the order of 1 cm , that mainly concern this chapter. 

This comprehensive review of theoretical models and techniques will be invaluable to theorists and experimentalists in the fields of infrared and Raman spectroscopy, nuclear magnetic resonance, electron spin resonance and flame thermometry. It will also be useful to graduate students of molecular dynamics and spectroscopy. 

It is well established that disulfur difluoride (S2F2) exists in two isomeric forms, the nonplanar disulfane FSSF and the branched thiosulfoxide form p2S=S, with the latter found to be the more stable isomer. Both isomers have been characterized by microwave spectroscopy, mass spectrometry, infrared and Raman spectroscopy as well as photoelectron spectra [6] (and refer-... 

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