Spectroscopies Raman

Raman scattering occurs as a result of a dipole moment induced in the molecule by incident light. Thus, if an atom or molecule is placed in a static electric field (E) such as is produced by passage of light, a dipole moment ([jl) will be induced as a result of the displacement of the nucleus 

In the study of minerals and other geological materials, Raman spectroscopy has been applied for chemical analysis and in studies of molecular and crystal structure, and of elastic and thermodynamic properties. A particularly important field for the application of Raman spectroscopy in chemical analysis is in the study of fluid inclusions in minerals, where the Raman microprobe has been developed to enable nondestructive in 

The effects of substitution of the different metals on the distribution of silicate species has been investigated not only for Ca/Mg substitution in the CaO-MgO-SiOj system, but also for a wide range of other silicate 

Raman scattering light is usually measured, because intensity of the anti-Stoles Raman scattering is relatively very weak. 

Raman spectroscopy is primarily a structural characterization tool. The spectrum is more sensitive to the lengths, streng ths, and arrangement of bonds in a material than it is to the chemical composition. The Raman spectmm of crystals likewise responds more to details of defects and disorder than to trace impurities and related chemical imperfections. 

Photomultipliers are used as detectors in the single-channel instruments. GaAs cathode tubes give a flat frequency response over the visible spectrum to 800 nm in the near IR. Contemporary Raman spectrometers use computers for instrument control, and data collection and storage, and permit versatile displays. 

Diode Array and Charge-Coupled Detector Systems 

Liquids and solutions can be measured in special cells that have optical windows at right angles, or they can be contained in capillary tubes or small vials. The latter are 

Intensity enhancement takes place on rough silver surfaces. Under such conditions, Raman scattering can be measured from monolayers of molecular substances adsorbed on the silver (pyridine was the original test case), a technique known as surface-enhanced Raman spectroscopy. More recendy it has been found that sur-fiice enhancement also occurs when a thin layer of silver is sputtered onto a solid sample and the Raman scattering is observed through the silver. 

Raman spectroscopy is a non-destructive technique that is used in cosmochemistry for identification of minerals and to evaluate the bonding and composition of organic molecules. The technique does not require special sample preparation raw rock samples, polished sections, fine-grained powders, and liquids can be analyzed. Raman spectroscopy is the basis for several instruments that are under consideration for upcoming NASA missions. 

Raman Spectroscopy. Raman spectroscopy of steroids offers considerable promise as a technique for structural studies, complementing i.r. spectroscopy. Vibrations of the non-polar parts of the steroid molecule dominate in the Raman spectrum, and olefinic and aromatic systems are especially prominent. Tetra-substituted olefinic bonds [e.g. which are not readily identified by other 

Nuclear Magnetic Resonance. Ziircher s massive compilation of chemical shifts of 18-H and 19-H signals, and increments produced by structural features in the steroid nucleus, is augmented by the publication of similar data for 344 steroids obtained by microbiological hydroxylations, and subsequent transformations. The compounds are mainly 5a-androstane derivatives, and include hydroxy- and oxo-functions at almost all the ring positions, as well as their derivatives and polyfunctional compounds. Solvent shifts are also reported. A set of diagrams illustrates the profiles and chemical shifts of signals due to methine protons in the C/fOH system at all the main steroid positions.  

Large chemical shifts when certain lanthanide complexes are added to solutions of alcohols, or of other compounds with available lone-pairs, offer promise for detailed analysis of spectra, and for structure determination. Tris-(2,2,6,6-tetramethylheptane-3,5-dionato)europium shifted the 4-methyl signals in lupeol 

Long-range couplings through four r-bonds cause separate splittings of the C-19 protons in the 3)8,19-ether (14). H, is coupled with 1-H, and Hb with 5a-H, each interaction involving a suitable planar zig-zag of tr-bonds (14 thickened lines). 

Gramain, H.-P. Husson, and P. Potier, Bull. Soc. chim. France, 1969, 3585. 

Raman spectroscopy gives results similar to those from infrared spectroscopy. This is why Raman spectroscopy is often used together with infrared spectroscopy in order to receive additional information about the sample analyzed. The motions of the molecule involved in the analysis of the sample in Raman spectroscopy are similar to those by infrared spectroscopy. These include rotational and vibrational motions. However, the physical causes of the resulting spectrum are different. 

The Raman effect used in Raman spectroscopy arises from the interactions of monochromatic radiation with the shell atom. In contrast to infrared spectroscopy, these interactions are independent of the wavelength of the light used for the analysis. 

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Most of the component parts used in Raman spectroscopy such as the monochromator and sample chamber have the same functioning principle as in infrared spectrometers. All these were described in detail in section 2.2.1. 

Raman spectroscopy is a technique for smdying molecular vibrations by light scattering. Raman spectroscopy complements IR absorption spectroscopy because some vibrations, as we have seen, do not result in absorptions in the IR region. A vibration is only seen in the IR spectmm if there is a change in the dipole moment during the vibration. For a vibration to be seen in the Raman spectmm, only a change in polarizability is necessary. 

In the Raman and i.r. spectra of crystalline methyl 3,6-dideoxy-/3-D-ri o-hexo-pyranoside measured at low temperatures, four O-H bands were observed in the O-H stretching region. These were correlated with four distinct hydrogen bonds determined from X-ray data, and deuterium-isotope dilution methods were used to assist the analysis. An interesting study of the far-i.r. spectrum of a pyroelectric sucrose single crystal has been carried out, and the temperature dependence was correlated with polarization of the low-frequency mode (49.5 cm ) along the binary axis.  

Studies of carbohydrates in solution have included an investigation of the intramolecular hydrogen bonding of methyl 4,6-O-benzylidene-a-D-hexopyrano-side derivatives. Diols, monomethyl ethers, and monodeoxy-compounds with various configurations were studied in the 3600 cm region. A similar investigation was carried out on methyl ethers and benzylidene derivatives of D-aldo-pyranoses. A laser Raman study of D-fructose in aqueous solution indicated that furanose forms could be distinguished from pyranoses and that at equilibrium the ratio of the two forms was 41 59.  

Raman spectroscopy probes the vibrational states of a molecule in a very different way to IR. The photon energy used is much higher (in the visible or UV part of the spectrum) and so causes an electronic rather than vibrational excitation. The light source will be 

The ability of Raman spectroscopy to give information on the vibrational states of a molecule depends on the role of the vibrational states during the relaxation processes that occur during the scattering event. We will see in the rest of this section that the energy of the scattered photon can differ from that of the incident radiation by an amount linked to the energy of the vibrational states of the molecule. In Raman spectroscopy, the measured frequency differences correspond to the frequencies of the vibrations of the molecules. Of course, not aU vibrational modes will be observed since there is a selection rule that controls which modes of a molecule are Raman active. 

Compressing the bond leads to a rapid increase in energy, as the nuclear repulsion between the two atom centres overrides the attraction between them due to the electronic bonding states. The origin of these bonding states will be covered in more detail in Chapter 7. 

If the molecule is stretched relative to the Morse curve minimum point, the energy again rises as the atoms begin to separate and their bonding interactions weaken. At large separations the two atoms would not be bonding at all and the Morse curve goes to zero. 

We can now show how the vibrational states can affect relaxation after an electronic excitation. If an electron is excited by the absorption of a photon it will move to a higher electronic state (be that real or virtual ) and so interact differently with the nuclei and other 

Raman spectroscopy is a suitable and direct technique that provides information on secondary and tertiary protein structures [23-26]. It is a powerful tool for investigation of protein structure in solid and liquid food systems in general [14, 27, 28], and for determination of the protein structure in muscle foods (meat or fish) in particular [15-18]. The spectral assignments of protein Raman bands are usually based on model compoxmds such as amino acids or short peptides. 

Changes in the frequencies, half-widths and intensities of the Raman bands of protein chemical groups mainly give information about changes in secondary protein structure (amide conformation region, C-C stretching vibration), while modifications 

Raman spectroscopy and Fourier Transform Raman spectroscopy (FTRS) [314,315] can detect vibrational motion in polymers but are less commonly employed in polymer blend characterization than FTIR nevertheless they offer utility in characterization of crystalline polymer morphology, conjugated polymers, thin film properties and surface modification as well as in 

Excimer fluorescence involving a complex (excited state-ground state) between adjacent or non-adjacent fluorescent units with the same polymer chain or intermolecular association between units on different chains can also be studied to assess phase behavior and the level of mixing in polymer blends. These studies generally involve the addition of low concentrations of aromatic polymers (capable of fluorescence) to non-fluorescent polymers. Excimer fluorescence is favored by phase separation, because the intermolecular associations of the fluorescent polymer will be shielded by the miscible non-fluorescent polymer, in which case monomer emission will be more dominant. This technique was developed and demonstrated initially by Frank and coworkers [333-335]. 

The experimental method to assess the phase behavior is to measure the ratio of excimer to monomer intensity, la/lm- Samples of the polymer blend are cast on sapphire disks at thicknesses of the order to 10-25 pm, and the fluorescence spectra are obtained. In a study of the excimer fluorescence of poly(2-vinyl naphthalene) (P2VN) in polystyrene, the monomer emission peak at 337 nm was compared with the excimer emission peak at 398 nm [334]. The ratio of the peaks versus polystyrene molecular weight is illustrated in Fig. 5.32 (a and b). Phase separation (at 0.3 wt% P2VN addition) was observed at PS Mn of 17,500. It was noted that the results show the onset of phase separation before any visual phase separation was observed. 

The dependence of la/Im of P2VN in a series of polyacrylates, PS and PVAc versus the host polymer solubility parameter showed a strong minimum at 8.85 caP/ /cm / [335]. Poly(2-isopropenyl naphthalene) (P2IPN) blends with PMMA and poly(n-butyl methacrylate) showed a marked change from 100% monomer emission to 70% excimer emission as the degree of polymerization of P2IPN increased above 20 [336]. PS excimer fluorescence 

Although not directly related to the subjects of NRET and excimer fluorescence, a study involving fluorescence polarization deserves mention in this section. Acenaphthylene labeled poly(acrylic acid)(PAA) was blended with PEO and the complexation formation was observed by fluorescence polarization [341]. The results showed the complex formation restricts the mobility of the PAA chain, is favored for high molecular weight PEO, and a small degree of neutralization of the PAA carboxylic acid groups is capable of breaking the complex. 

Raman spectroscopy is a good technique for qualitative analysis and discrimination of organic and/or inorganic compounds in mixed materials. A Raman spectrum can be obtained from samples that are as small as 1 xm. The intensities of bands in a Raman spectrum depend on the sensitivity of the specific vibrations to the Raman effect and are proportional to concentration. Thus, Raman spectra can be used for semiquantitative and quantitative analyses. The technique is used for identification of organic molecules, polymers, biomolecules, and inorganic compounds both in bulk and as individual particles. Raman spectroscopy is particularly useful in determining the structure of different types of carbon (diamond, graphitic, diamond-like-carbon, etc.) and their relative concentrations. 

Since the Raman scattering is not very efficient, a high power monochromatic excitation source is required as provided by a laser beam Ar 488.0 and 514.5 nm HeNe 633 nm are used, although Nd YAg 1.064 nm is more intense but FTIR must be used and this overcomes problems with fluorescence. 

Although IR and Raman are complementary techniques, Raman spectroscopy can resolve 1-2 pm and can be focussed to a beam about 2.5 pm in diameter, whereas IR cannot 

In Raman spectroscopy (cf., e.g., [183-187]), the strayUght spectrum is recorded of a sample which is irradiated with monochromatic light (produced, e.g.,by a laser). A schematic representation of the Raman scattering experiment is shown in Fig. 10. 

In fact, the experimental pioneering work of Raman spectroscopy in zeolite research, viz. of hydrated microporous materials, was published by Angell [187] as early as 1973. Since that time the interest in utilizing this technique for mole- 

As large single crystals are frequently unavailable for synthetic zeoHtes, most of the Raman spectra have been taken from powdered samples without polarization. Minimum sample sizes of about 1 mm are required for conventional Raman techniques. 

One more advantage of Raman spectroscopy is due to the fact that the Raman spectrum of water exhibits only a few signals of low intensity. Thus, careful dehydration of zeolites, which is crucial in many IR experiments, does not play the 

However, a detailed discussion of the progress in Raman studies of adsorbed molecules is beyond the scope of this chapter, and we therefore refer to previous extended reviews [194, 195]. In subsequent sections we will focus on some selected studies dealing with Raman spectroscopy. Fimdamentals of Raman spectroscopy especially in surface research including zeolites are treated, e.g., in Refs. [ 183,185]. Examples of application of Raman spectroscopy in zeoUte research are provided, for instance, in Sects. 5.2 (frameworks), 5.3 (extra-framework cations), 5.S.2.7 (adsorption of complex molecules) and 5.6.2 (zeolite synthesis and crystallization). 

In Raman spectroscopy, the spectrum of light inelastically scattered by a sample is registered. This process is called Raman scattering (RS) if the frequency of the incident light is in the visible region of the spectrum and the frequency shift observed in scattering corresponds to vibrational or rotational transitions of the material. Raman spectra are widely used for the identification of chemical compounds in the sample as well as for the study of vibrational dynamics. Similar to photoluminescence spectroscopy, Raman spectroscopy is not 

and Raman Spectroscopy. I.r. and Raman spectra have been measured for H. W. Gibson, Canad. J. Chem., 1973, 51, 3065. 

Laser Raman spectroscopy uses a light scattering process where a specimen is irradiated monochromatically with a laser. The visible light that has passed into the specimen causes the photons of the same wavelength to be scattered elastically, while 

Raman and IR spectroscopies are complementary to each other because of their different selection rules. Raman scattering occurs when the electric field of light induces a dipole moment by changing the polarizability of the molecules. In Raman spectroscopy the intensity of a band is linearly related to the concentration of the species. IR spectroscopy, on the other hand, requires an intrinsic dipole moment to exist for charge with molecular vibration. The concentration of the absorbing species is proportional to the logarithm of the ratio of the incident and transmitted intensities in the latter technique. 

As the laser beam can be focused to a small diameter, the Raman technique can be used to analyze materials as small as one micron in diameter. This technique has been often used with high performance fibers for composite applications in recent years. This technique is proven to be a powerful tool to probe the deformation behavior of high molecular polymer fibers (e.g. aramid and polyphenylene benzobisthiazole (PBT) fibers) at the molecular level (Robinson et al., 1986 Day et al., 1987). This work stems from the principle established earlier by Tuinstra and Koenig (1970) that the peak frequencies of the Raman-active bands of certain fibers are sensitive to the level of applied stress or strain. The rate of frequency shift is found to be proportional to the fiber modulus, which is a direct reflection of the high degree of stress experienced by the longitudinally oriented polymer chains in the stiff fibers. 

Enabled by the high resolution of spectra, which is enhanced by the use of spatial filter assembly having a small (200 pm) pin hole, the principle of the strain-induced band shift in Raman spectra has been further extended to the measurement of residual thermal shrinkage stresses in model composites (Young et al., 1989 Filiou et al., 1992). The strain mapping technique within the fibers is employed to study the 

Intensity ratio of Raman bands f(A]g)//(E2g) and the corresponding apparent crystal diameter, L. for various carbon fibers  

As an example of a Raman spectrum from a liquid a recording for CH2CI2 is shown in Fig.6.69. Raman spectra for gases will be discussed in Sect. 10.1.3. 

The Raman scattering can be enhanced by a factor of the order of 10 if the exciting line coincides with an allowed electronic transition (resonance Raman effect). During recent years several types of coherent Raman spectroscopy [6.127] have been introduced, e.g. coherent anti-Stokes Raman spectroscopy (CARS) (Sects.8.6 and 10.1.4) and Raman gain spectroscopy. 

Although Raman spectroscopy does not employ absorption of infrared radiation as its fundamental principle of operation, it is combined with other infrared spectroscopies into a joint section. Results obtained with various Raman spectroscopies as described below cover vibrational properties of molecules at interfaces complementing infrared spectroscopy in many cases. A general overview of applications of laser Raman spectroscopy (LRS) as applied to electrochemical interfaces has been provided [342]. Spatially offset Raman spectroscopy (SORS) enables spatially resolved Raman spectroscopic investigations of multilayered systems based on the collection of scattered light from spatial regions of the samples offset from the point of illumination [343]. So far this technique has only been applied in various fields outside electrochemistry [344]. Fourth-order coherent Raman spectroscopy has been developed and applied to solid/liquid interfaces [345] applications in electrochemical systems have not been reported so far. 

Fundamentals. Provided enough substance is present at the electrochemical interface in a fairly thick film of corrosion products or in a modifying layer, identification of the constituent matter is possible with (normal) Raman spectroscopy (NRS). Although this approach is not exactly surface specific, it is included because it has been applied frequently. The same argument applies to Raman spectroscopy applied with the help of a microscopy (Raman microscope). 

The discovery of a particular enhancement effect (up to 10 ) that affects only species in close contact with the metal electrode surface (i.e. adsorbed species) by Fleischmann et al. [352] and slightly later by Jeanmaire et al. [353] and a report on the utilization of resonance enhancement in surface Raman spectroscopy [354] demonstrated surprisingly the feasibility of vibrational studies of electrochemical 

Scattered light is observed in all cases only when the polarizability of the illuminated species changes during the involved vibrational mode (Raman selection rule) [165, 205]. 

CT refers to charge transfer because some explanations of the chemical enhancement effect assume a charge transfer between the metal and the adsorbate, resulting in the observed enhancement of scattered Raman radiation. 

Visible and UV absorption spectroscopy are based on studying that part of the incident light transmitted (after absorption) through an electrolytic solution in the same direction as the original beam. However, a certain amount of light is scattered in other directions. 

The problem with Raman spectroscopy is the low intensity of the Raman lines, which permits easy detection of species only in concentrated solutions. Fortunately, the availability of lasers, which are intense sources of monochromatic light, is stimulating further applications of this powerful technique, which is noted for the lack of ambiguity with which it can report on the species in an electrolytic solution. Devices that distinguish a low-intensity signal from noise also help. 

The physical basis of the Raman effect is related to deformation of electron shells of molecules in an electric field E determined by the molecular polarisability a. Because the laser beam can be considered an oscillating electromagnetic wave with the electrical vector E and a frequency v0 it induces during interaction with the sample the electric dipole momentum P = aE. This momentum is the driving force of the deformation of the electronic shells of the molecules. Because this deformation is periodical, the molecular dipoles begin to vibrate with a characteristic frequency vm. 

The oscillating dipoles emit light of three different frequencies. The conditions are as follows  

Raman Microscopy of Bioceramic and Photoactive Titania Coatings 

Like IR spectroscopy, Raman spectroscopy is a routine analytical technique that has been widely applied to CPs, and it is best to cite its use with specific examples. Most 

Raman studies of CPs to date have been under resonance conditions, since they have mostly used Visible region frequencies which lie witliin the strong absorption bands of the highly colored doped state of the CPs, or sometimes even beyond the bandgap. In certain cases, if the completely de-doped state of a CP is also studied along with doped states, then the former may correspond to non-resonance conditions while the latter corresponds to resonance conditions. An important attractive feature of Raman and resonance Raman spectroscopy is of course that it may be carried out in aqueous media and for powder samples as well. 

P(T) shows Raman active modes at 1500, 1458 (C=C antisymmetric stretch), 1045 (CH in-plane bending) and 700 cm (ring deformations) [421]. In P(3MeT), die C=C antisymmetric stretch is shifted to 1470 cm , and overtone and combination bands associated with this mode, which are taken as an indication of a high degree of order in the CP [422]. 

Kastner et al. [428] recently carried out a resonance Raman study of poly(thieno-pyrazine), a low bandgap CP which has a pyrazine ring fused onto a thiophene ring. They observed two strong bands, 1520 and 1560 cm, associated with the C=C stretching mode, which showed a frequency dispersion of 16 and 25 cm from 742 

Infrared and Raman spectroscopy are nondestructive, quick and convenient techniques for monitoring the course of solid-phase reactions, and have therefore been widely used for the characterization of polymer supports and supported species [156-160]. In fact, the application of infrared spectroscopy in solid-phase synthesis has received much attention and has been the subject of several recent reviews [127, 128, 161-164]. Reactions involving either the appearance or disappearance of an IR-active functional group can be easily monitored using any of the IR techniques described in this section. Some beads are typically removed from the reaction mixture, then they are quickly washed and dried prior to IR analysis. Traditionally, polymer supports are diluted and ground with KBr, then conventional FT-IR analysis of the KBr disk is carried out Although this is a commonly used 

FT-IR microspectroscopy is a new nondestructive, fast and rehable technique for solid-phase reaction monitoring. It is the most powerful of the currently available IR methods as it usually requires only a single bead for analysis, thus it is referred to as single bead FT-IR [166]. (See also Chapter 12 for further details). The high sensitivity of the FT-IR microscope is achieved thanks to the use of an expensive liquid nitrogen-cooled mercury cadmium telluride (MCT) detector. Despite the high cost of the instrument, this technique should become more widely used in the future as it represents the most convenient real-time reaction monitoring tool in SPOS [166, 167]. 

The kinetics of solid-phase reactions have also been investigated by Yan and coworkers [166, 169]. The relative intensities of the IR bands that either disappear or develop during the reaction (compared with an internal reference polymer band) can be plotted against time. This approach can be used to determine when the reaction has reached completion. 

In situ IR spectral monitoring of solid-phase reactions carried out in dichloro-methane, using a flow-through cell [170, 171] has also been described. 

Further kinetic studies [172] have focused on the comparison of the rates of reactions on a solid support and in solution-phase, and have served to demonstrate that solid-phase reactions are not always slower than those in solution-phase. 

Infrared and Raman spectroscopy are often grouped together, since both techniques provide information on the vibrational modes of a compound. However, since the two spectroscopic techniques are based on different physical principles the selection rules are different. Infrared spectroscopy is an absorption phenomenon, while the Raman spectroscopy is based on a scattering phenomenon (Raman and Krishnan 1928). In general, infrared energy is absorbed by polar groups, while radiation is more effectively scattered in the Raman effect by symmetric vibrations and nonpolar groups (Colthup et al. 1990 Ferraro and Nakamoto 1994). For most molecules other 

A typical example of the characterization of a polymorphic system by FT Raman spectroscopy has been given by Gu and Jiang (1995) while an application of the technique with near infrared excitation to the polymorphic cimetidine system has been described by Tudor et al. (1991). The FT Raman technique has been compared to infrared diffuse reflection spectroscopy in the study of the polymorphs of spironolactone (Neville et al. 1992), and the pseudopolymorphic transition of caffeine hydrate (i.e. loss of solvent) has been monitored using the technique (de Matas et al. 1996). 

Some of the previous references contain descriptions of the use of Raman spectroscopy for quantitative analysis of mixtures of polymorphs. Additional examples may be found in Deeley et al. (1991), Petty et al. (1996), Langkilde et al. (1997), Findlay and Bugay (1998) and Bugay (2001). 

7 Solid state nuclear magnetic resonance spectroscopy 

The differences between the IR and Raman spectra were examined as long ago as the 1930s. Mousseron later performed measurements on many oxiranes and identified the individual vibration bands. More recently, the results of solid-, liquid-, and gas-phase studies on the Raman spectra of alkyl- and vinyl- substituted oxiranes have been reviewed. 

The condition for a molecule to be Raman active is a change in the polarization (deformation) of the electron cloud during the interaction with the incident radiation. In case of Raman scattered radiation, the magnitude of the field vector E of the exciting radiation is modulated by the molecular vibrations. The induced dipole moment /t is 

The Raman method is the complementary method to IR spectroscopy, where the excited vibrational state is directly approached. The Raman spectrum is the plot of Raman intensity versus Raman shift Raman band parameters are the band position in the spectrum (Raman shift), the intensity of the band and the band shape. As in the case of the IR spectrum, the features of a Raman spectrum (number of Raman bands, their intensities and their shapes) are directly related to the molecular stracture of a compound. 

The complementarity of IR and Raman spectra is based on the different excitation conditions change of dipole moment (vector quantity) in the case of an IR spectrum, change of polarization (tensor quantity) in the case of a Raman spectrum. Since a tensor is a three-dimensional quantity, the depolarization ratio p can be obtained by measuring Raman spectra with polarized Hght (polarization directions parallel and perpendicular to the optical plane  

UV/VIS absorption and luminescence spectra are related to electronic and vibrational transitions. The term luminescence summarizes a combination of basic processes like fluorescence or phosphorescence, which are described below. Transitions occur between energy levels described like S t, where S indicates an electronic singlet state and n v the corresponding electronic (n) and vibrational (v) excitation levels. The intensity of a transition from an electronic and vibrational ground state Sq o to a corresponding excited state S is proportional to the square of the transition dipole moment M, which itself can be separated into an electronic part Mq and the vibrational contribution Fo q.  

v represents the so-called vibrational overlap integral of the vibronic wave-functions xo.o and Xn,v, given by 

For many years Raman spectroscopy has been a powerful tool for the investigation of molecular vibrations and rotations. In the pre-laser era, however, its main drawback had been lack of sufficiently intense radiation sources. 

The introduction of lasers therefore has indeed revolutionized this classical field of spectroscopy. Lasers have not only greatly enhanced the sensitivity of spontaneous Raman spectroscopy but they have furthermore initiated new spectroscopic techniques, based on the stimulated Raman effect, such as coherent anti-Stokes Raman scattering (CARS) or hyper-Raman spectroscopy. The research activities in laser Raman spectroscopy have recently shown an impressive expansion and a vast literature on this field is available. In this chapter we summarize only briefly the basic background of the Raman effect and. present some experimental techniques which have been developed. For more thorough studies of this interesting field the textbooks and reviews given in [9.1-4] are recommended. 

This has enabled Raman spectroscopy to be used routinely for the identification of polymer types and the analysis of contaminants within polymer samples. 

When it comes to analysing small samples, sample surfaces or contaminants in samples, the scanning electron microscope (SEM)/XRF combination (sometimes referred to as energy dispersive analysis (Edax)) can be a very valuable tool. 

Raman scattering forms the basis for a type of spectroscopy, called Raman spectroscopy. Today, Raman spectroscopy is performed using lasers as the incoming light source because the laser light is intense (providing a better chance to observe photons that have shifted frequency) and monochromatic (making it easier to find shifted-frequency photons).  

Unless otherwise noted, all art on this page is Cengage Learning 2014. 

FIGURE 14.39 A Raman spectrum of tetrafluoroethylene, CFjCFj. The difference between the frequency of the emitted photon and the excitation photon equals an energy of vibration of the molecule. The Stokes lines and anti-Stokes lines are modified mirror images of each other, reflected through the excitation frequency. Anti-Stokes lines are always lower in intensity than the corresponding Stokes line. 

Raman spectroscopy also has selection rules. The gross selection rule for a Raman-active vibration is related to the polarizability of the molecule. Polarizability is a measure of how easily an electric field can induce a dipole moment on an atom or molecule. Vibrations that are Raman-active have a changing polarizability during the course of the vibration. Thus, a changing polarizability is what makes a vibration Raman-active. The quantum-mechanical selection rule, in terms of the change in the vibrational quantum number, is based on a transition moment that is similar to the form of M in equation 14.2. For allowed Raman transitions, the transition moment [a] is written in terms of the polarizability a of the molecule  

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Raman spectroscopy is particularly well suited for use in process monitoring and conttol. This chapter discusses Raman spectroscopy s attractive features as well as alerts the reader to aspects that may present ehallenges. The fundamental principles of the technique are reviewed. The reader will learn about instrumentation and options in order to make the most appropriate choices. Special aspects of performing quantitative Raman spectroscopy are discussed since these are required in many installations. Apphcations from many diverse fields are presented. The reader is encouraged to examine aU of the areas since there are good lessons and stimulating ideas in aU. 

Raman spectra encode information about a sample s molecular stracture and chemical enviroiunent. Fortunately, that information is readily accessible since Raman speetroscopy is an extremely flexible technique, both in what it can measure and how the measurements ean be made. 

As we have previously noted, Raman spectroscopy is complementary to IR spectroscopy. A special feature of Raman spectroscopy is that molecules without a dipole moment can be investigated, e.g. H2, N2, and O2. In early Raman spectroscopy measurements a strong Hg lamp was used as a light soiu ce. In modern commercial instruments an Ar laser (Sect. 8.4.5) with an 

Group Wave niunber [cm J Group Wave number [cm ] Group Wave number [cm- ] 

In the previous section we have described how optical spectroscopy can be used to analyse samples in the laboratory. In this section we will describe how spectroscopy can provide information on the environment by performing measurements at a distance. Remote sensing is a general term used for 

Fourier transfer near infrared Raman spectroscopy (400-10,000 cm ) is useful for the examination of additives in polymer extracts [31]. 

An example of the application of Raman spectroscopy is the identification of additives in fire retardant PR When a sample of PP was examined by IR spectroscopy the strongest bands (9.8 and 14.9 pm) were due to a talc-type material and bands of medium intensity were assigned to PP and possibly antimony trioxide (13.4 pm). Additional weak bands in the 7.S-7.7 pm region were possibly due to decabromodipbenyl ether. In the Raman spectrum, however, the strongest bands (250 and 185 cm shift) confirmed the presence of antimony trioxide and some bands of medium intensity confirmed the presence of decabromodipbenyl ether (doublet at 140, triplet at 220 cm shift) and PP (800, 835, 1150, 1325, 1450 and 2900 cm shift). The silicate bands that obscured the regions of the IR spectrum were not observed in the Raman spectrum. 

Although both of these spectroscopic methods have a wide use in their own right, this example demonstrates well the complementary value of the two methods, taking advantage of the fact that elements of high atomic number, e.g., antimony and bromine, have relatively more intense Raman spectra but the lighter elements show up clearly in the IR spectra. 

Other applications of Raman spectroscopy inclnde monomers in polymethylmethacrylate [32] and additives in PVC [33]. 

The general principles involved in Raman spectroscopy are described in section 2.6. This method for characterising orientation is very similar to the fluorescence method, in that it involves both incident and emerging radiation, but the Raman process is a scattering process the re-radiation is essentially instantaneous. It is also similar to the infrared method in that it is associated with molecular vibrations and it has the same advantages of potential selectivity to a part of the polymer molecule or a phase of the polymer. 

The theory of the method is rather complicated, because the amplitude of Raman scattering is described by a second-rank tensor, so it will not be discussed here. Just like for fluorescence, P2 cosff)) and (P4(cosd)), or cos 6) and (cos 6), can, at least in principle, be obtained for the simplest type of uniaxial orientation distribution and these values now refer directly to the molecules of the polymer itself. In practice it is often necessary to make various simplifying assumptions. For biaxially oriented samples several other averages can be obtained. 

Bakhshiev developed a method for the determination of ground- and excited-state dipole moments based on Raman spectra which has been successfully used for different compounds [55-57]. 

Classify the following molecules according to the general characteristics expected for their infrared and Raman spectra (a) CI2 (b) HCl (c) CO (d) CF2=CH2 

Solution Raman spectroscopy is often used in conjunction 

the two identical atoms exert equal and opposite electronegative effects upon each other. Hence the infrared spectrum of Cl2 will show no absorptions and the Raman spectrum will show a strong Cl-Cl absorption. 

Note Resonance structures do not exist independently they only approximate what the molecule really looks like. That is, the molecule is actually a hybrid of the resonance structures. 

The principal characteristic of the infrared and Raman spectra will be the strong C=0 stretch. 

Infrared Absorption Bands of PFSA-Na+ lonomer and Raman Spectroscopy Peaks of PFVESF Precursor (870 g/mol) 

Band Position (cm ) Assignment Band Position (cm ) Assignment 

Perusich performed detailed FT-IR study of the sulfonyl fluoride, potassium salt, and sulfonic acid forms of Naflon and established the FT-IR method to determine the equivalent weight (EW) of PFSI. For thin films ( 1.1 mil), the EW of PFSI can be obtained by calibrating the C-F/C-O-C absorbance band ratio. While for thick films (5-25 mil), the EW of PFSI can be obtained by calibrating the C-F/-SO2F absorbance band ratio. 

Attenuated total reflection (ATR) is a useful method to study the surface structural of PFSA membrane, and it can circumvent the film thickness problem. Liang found that v XCFj), Vs(CF2), and v/SO) of ATR spectra are red shifted by 20.4, 10.7, and 4.8 cm compared with that of transmission IR, which indicates that chemical environment is different for membrane surface and bulk.  

And Table 2.3 lists the maxima of the lines observed in the Raman spectrum and their assignments. These peak positions correlated well with results obtained by Gruger. f As for PFS A ionomer, the peaks due to SOj should appeared at 1060 cm vXSOf) and 1216 cm (SOs ). 

The combination of atomic force microscopy (AFM) and Raman spectroscopy is another approach to attain high spatial resolution. AFM also employs a sharp tip close to a sample surface. When the tip is made of metal and light is irradiated onto the tip and surface, Raman scattering is largely enhanced. In this way, a spatial resolution of 15 nm is achieved [2]. 

In actual experimental setup for the combination of STM with Raman spectroscopy, there are essentially two optical detection methods as shown in 

For Raman scattering measurement, a freshly cleaved sample is directly illuminated with the Ar-ion laser, and the resulting spectrum, accumulated during 10 min, is shown in Fig. 23. The band at 1580 cm 1 corresponds to the in-plane C-C breathing mode of the whole graphite lattice, namely the E2g mode. The band at 2730 cm-1 is an overtone of a lower-energy vibration, and 

All carbon allotropes [not only fullerenes and CNTs, but also amorphous and crystalline carbon-like diamond, graphite, and CNTs] are Raman active. In particular, the crystalline forms of carbon exhibit sharp Raman bands that make them clearly distinguishable from the other carbon allotropes. 

In fact, Raman spectroscopy has proved to be one of the most important techniques for the characterization of SWCNTs and is, therefore, extensively used to characterize both solid and solution phase CNT samples.For instance, this analytical technique may provide information on their chirality, their diameter distribution, or even their orientation.  

It has been shown that at fixed laser energy, intertube interactions in bundles involve broadening and red-shifting of the interband transition [e.g., RBM bands]. The amplitude of this peak is strongly related to the inter-tube contact area, as well as to the orientation and compositional disorder in the sample. - - This is why Raman 

On the contrary, this technique is much less suitable for the characterization of MWCNTs. The signal is generally weak and the features broad, with relatively poor definition. Both factors significantly hinder the readability and analysis of the spectra obtained. For example, RBM features which are well-defined in good resonance conditions for small diameter tubes (typically smaller than 2 nm) are usually weak and poorly resolved due to band broadening caused by the large range of diameters of a MWCNT sample.  

The major area of application for solids and liquids is chemical fingerprinting and the identification of unknown compounds. For solids, Raman is also used for phase identification, following amorphous/crystalline transitions, measurement of stress and strain, and, in the microscope mode, the detection and analysis of defects, including particles during wafer processing. 

Typically, because the exciting radiation can be at any frequency, Raman spectroscopy utilizes monochromatic laser sources and the scattered light is collected at an IR detector. 

For example, as noted above, ethene (ethylene, CH2=CH2) lacks absorption in the carbon-carbon double-bond region of the IR spectrum because of its symmetry. In the Raman, however, ethene (ethylene, CH CH2) absorbs strongly at about 1580 cm In more complicated cases, it may be that there are some vibrational modes that affect both the polarizability and the dipole moment (present in molecules not electrically symmetrical), and molecules within which these modes are present may have similar absorbances in both the IR and Raman. 

Examination of such spectra allows one to obtain distances between nuclei and the shapes of molecules from moments of inertia (i.e., I = m r, where m. is the reduced mass and r is the internuclear distance). Further, as already pointed out in Chapter 1, application of a constant electric field while the spectrum is being observed causes the energy levels to shift by an amount due to the molecular dipole moment, p. 

Since the measurement of frequencies can be made with high precision, the technique is very valuable. Regrettably, it is only applicable to gases that have a permanent electric dipole moment and so its utility is limited. 

Among the more interesting examples of the use of this technique has been the analysis of methanol (methyl alcohol, CFI3OFI) in the presence of both ethanol (ethyl alcohol, CF13CFI20FI) and water (H2O). The former has a series of bands in the microwave spectrum lying between 29,636.91 and 37,703.67 MHz that are unique, and quantitative measurements of these have been used to determine the amount of methanol (methyl alcohol, CH3OH) in various samples of wine.  

In general, this is a bnlk technique with the capability of measuring surface species as well. The information is parallel and complementary to that obtained by FTIR spectroscopy, providing information on functional groups and specific bonds [25,26]. 

Another laser based technique, which may be used together with time-resolved luminescence, is Raman spectroscopy. It is very well known technique, which is widely used in mineralogy. Several reviews have been recently published mostly devoted to minerals (Dubessy et al. 1994 Nasdala et al. 2004 Smith and Dent 2005 Jasinevicius 2009 Dubessy et al. 2012 Panczer et al. 2012). Thus only the theoretical aspects which are the mostly relevant to our research devoted to the real time online quahty control of minerals will be considered. 

The physical origin of Raman scattering may be viewed from a simple classical perspective in which the electric field associated with the incident light interacts with the vibrating crystal. In particular, this interaction occurs through the 

Wave model of Raman scattering may be shortly presented by the following way. A beam of radiation having the frequency Vex is incident upon a mineral. The electric field E of this radiation can be described by the equation  

When the electric field of the radiation interacts with the electron cloud of the mineral bond, it induces a dipole moment m in that bond that is given by 

Extending the equation of polarizability with that of the intemuclear separation, and by substituting the initial equation of the dipole moment, one obtains an expression for the induced dipole moment m  

Modulation techniques have been shown to be capable of increasing the signal-to-noise ratio for Raman spectroscopy, this being illustrated for the resonance-enhanced inverse Raman effect.Inverse Raman spectroscopy enables spectra of highly luminescent systems to be recorded. A suitable spectrometer has been described in which a resolution of 1 cm was achieved with scan rates dependent only upon the scan speed of the dye laser used for excitation.A 100-fold increased sensitivity was reported with the use of a multiplex spectrometer for 

Raman measurements. Two high-pressure cells for Raman spectroscopy have been reported allowing pressures up to 345Kbar with some temperature variation. -  

Progress in the Raman spectroscopic study of carbohydrates became possible during the past few years owing to the introduction of laser sources. Before discussing the results of laser-Raman spectroscopy applied to carbohydrates, we shall give a brief recapitulation of the physical principles of the Raman effect. Experimental techniques of infrared spectroscopy have been described in previous reviews,116,17 but no such description has been given for the Raman method. That is why the Description Section, which follows, will include the physical fundamentals of the method, as well as the sampling techniques. 

As may be seen in Fig. 14 when the incident radiation, of frequency v0, falls on the molecule, the molecule is raised to a virtual state. The only requirement of this virtual state is that it does not correspond to an electronic-energy level of the molecule. From this virtual state, the molecule can either 

In addition to the intensity and frequency of the Raman lines, the polarization character of the lines can be measured. In fact, what led Sir C. V. Raman to believe that he was observing a new phenomenon was the unique polarization properties of this new radiation. Usually, the observations are made perpendicular to the incident beam, which is plane-polarized, as at (a) in Fig. 15. The depolarization ratio p is defined as the intensity ratio of the two polarized components of the scattered light that are respectively parallel and perpendicular to the direction of the (polarized) incident beam when the polarization of the incident beam is perpendicular to the plane of propagation and observation (p = I /ll). 

Theoretically, 0=s p =s 3/4, depending on the nature and symmetry of the vibration. Nonsymmetric vibrations give depolarizations of 3/4. Symmetric vibrations give p ranging from 0 to 3/4. Accurate values of p are important for determining the assignment of a Raman line to a symmetric or an asymmetric vibration. 

In general, the signal-to-noise ratio for Raman spectra decreases as the molecular weight increases. This is due to the sensitivity of the Raman effect to the density of the sample. In addition to this effect, it has been found that, for polysaccharides, many vibrational modes cannot be separated the maxima observed can involve the merging of several neighboring maxima. Other experimental advantages, and some difficulties, will be listed after description of the sampling techniques. 

An excellent review on vibrational spectroscopy in supercritical fluids was published in 1995 by Poliakoff et al. [6]. In the late 1990s, Kessler et al. [7] developed IR and Raman spectroscopy for the investigation of rapid high-pressure reactions in optical cells. Raman was preferred to IR for the determination of the decomposition rate of peroxides under high pressure. They studied the decomposition of tert-butyl peroxypivalate at pressure up to 180 MPa and temperatures of 90-160 °C. A typical Raman spectrum is presented in Fig. 5.3. 

UV-Vis spectra are generally highly sensitive but less informative, because they typically consist of a few broad absorption peaks. Chemical reaction monitoring using UV-Vis spectroscopy is less common than using other spectroscopic techniques. Two major devices have been developed for supercritical fluids the fiber-optic and the cell device. Hunt et al. [9] reported the development of a fiber-optic-based reactor connected directly to a CCD array UV-Vis spectrometer for in situ determination of reaction rates in SCCO2. The cell can be configured either to study the kinetics of chemical reactions or to determine the rate of dis- 

The study of supercritical fluid systems by Nuclear Magnetic Resonance (NMR) has been accomplished in two ways the high-pressure probe method and the high-pressure cell method. At this present stage, no paper on the study of polymerization reactions in SCF by NMR could be found. Nevertheless, other reactions have been studied in supercritical media and at extreme conditions [13], and these can be compared with polymerization reactions. 

Fisher at al. [17] reported the use of on-line NMR spectroscopy with a flow probe for supercritical fluid chromatography (SFC) used for reaction monitoring purposes. They monitored aliphatic amines in SCCO2. A typical NMR spectrum reahzed both in classical media and in SCCO2 is presented in Fig. 5.6. 

They concluded that the use of on-line NMR spectroscopy employing an SFC probe enables the investigation of reactions in supercritical medium. 

The other vibrational spectroscopies, although less easily applied, may provide complementary structural information. Raman spectroscopy has been used to detect metal-metal bonds in metal oxide supported osmium [86] and iridium [87] clusters. This method might be expected to find application in the study of zeolite supported metal carbonyl dusters, but it is still far from routine since samples are subject to destruction by laser beams, and fluorescence often prevents measurement of useful spectra. 

The Raman spectroscopic technique relies on the abilities of a material to scatter light inelastically. Such scattering, known as Raman scattering, occurs when a photon excites a thermal mode of vibration in the molecule similar to those probed in infrared spectroscopy. For example, the excited mode could be a bond stretch or a rotation. The difference in this technique is that instead of the photon being fully absorbed, it is absorbed and then reemitted at a lower frequency. The change in frequency of the detected photon is equal to the resonant frequency of the excited vibrational mode. 

Raman spectroscopy data are usually plotted as a spectrum in terms of the wave number k (or Raman shift), measured in cm T The typical range of wave numbers probed is between 200 and 4000 cm-T For example, the OH stretch mode will have a wave number of 3400 cm k and the CH stretch has a wave number of 2290 cm-. To take a measurement, the wavelength intensity at different frequencies is collected and plotted as a function of the wave number. 

FIGURE 4.19 An example of an FTIR spectrum for three different example polymers poly(vinyl pyridine) (P4VP), polystyrene, and a poly(vinyl pyridine)-block-polystyrene (PS-b-P4VP). In the data shown, we can clearly see that the block copolymer has characteristics of both of its individual polymer block components. The C=C stretch mode is visible at about 1500 cm for all three molecules. 

Analysis of paints is a routine part of forensic investigations of hit-and-run accidents or collisions involving vehicles. Paints have complex formulations. Automotive paints are applied in layers and the sequence and colours of the layers provide information on the origins of the vehicle. By matching IR and Raman spectroscopic data from a vehicle paint sample to those in databases (e.g. the European Collection of Automotive Paints and Paint Data Query), it is possible to determine the vehicle s manufacturer and year of production. The main components of a paint fall into four categories  

Buzzini and W. Stoecklein (2005) in Encyclopedia of Analytical Science, 2nd edn, eds. P. Worsfold, A. Townshend and C. Poole, Elsevier, Oxford, p. 453 - Paints, varnishes and lacquers . 

Clark (1995) Chem. Soc. Rev., vol. 24, p. 187 - Raman microscopy apphcation to the identification of pigments in medieval manuscripts . 

Clark (2002) C. R. Chimie, vol. 5, p. 7 Hgment identification by spectroscopic means an arts/sciraice interface . 

Clark (2007) Appl. Phys. A, vol. 89, p. 833 - The scientific investigation of artwork and archaeological artefacts Raman microscopy as a structural, analytical and forensic tool . 

Camphorsulfonic acid doped polyaniline/ PE blends, prepared by mixing hot solutions of polyaniline in m-cresol and PE in decalin, have been studied using resonance Raman spectroscopy [46]. The results obtained showed that polyaniline treated with m-cresol maintained an extended conformation in the blends. The homogeneous regions of the blend samples exhibited bands at 1160 and 1173 cm which were attributed to polyaniline chains, indicating that polyaniline maintained its characteristics and conformations in the insulating PE matrix. Moreover, the lack of significant differences in the Raman spectra of the blends, compared to the spectra 

Yashino and Shinomiya [31] have published Raman spectra of solutions of various polymers. The technique has also found a limited application in structural studies of polymers [32-44]. For example, the three C=C stretching bands in poly butadiene corresponding to the three possible configurations can be observed by Raman spectroscopy. Raman spectroscopy has many applications in the identification of polymers in which additives obscnre the polymer peaks obtained in the IR spectrum. 

Raman scattering was first observed in 1928 and was used to investigate the vibrational states of many molecules in the 1930s. Initially, spectroscopic methods based on the phenomenon were used in research on the structure of relatively simple molecules. Over the past 20 years, however, the development of laser sources and new generations of monochromators and detectors has made possible the application of Raman spectroscopy to the solution of many problems of technological interest. 

In many industrial laboratories, Raman spectrscopy is routinely used, together with infrared spectroscopy, for acquisition of vibrational spectra. Raman spectrometer systems for routine analytical applications are commercially available. An important expansion of the potential of the technique has arisen from the use of the microprobe, which permits acquisition of spectra from domains as small as one micron. 

Application of Raman spectroscopy to lignin analytical chemistry is relatively new, and only limited information has been obtained. However, the technique offers several potential advantages and, though it is complementary to infrared spectroscopy, it gives information that is not accessible with the latter alone. 

Springer Series in Wood Science Methods in Lignin Chemistry (Edited by S.Y. Lin and C.W. Dence) 

A Raman spectrum is obtained by exposure of a sample to a monochromatic source of exciting photons and measurement of the frequencies of the scattered light. Because the intensity of the Raman scattered component is much lower than the Rayleigh scattered component, a highly selective monochromator and a very sensitive detector are required. 

The photons excite the molecules to a virtual electronic state, (Fig. 12.6a) from which emission occurs emission to the ground vibrational state is Rayleigh scattering. If the photons have a very high energy then the virtual state is within the vibration levels of the excited electronic state. In this case there is a much greater interaction between the radiation and the molecules and an increase in intensity of the Raman effect by a factor of 104-106—the resonance Raman effect (Fig. 12.6b). 

The resonance Raman effect has been applied to electrochemical cells, generally with laser excitation21,22. As it is possible to construct cells that are transparent to IR, it is not necessary to use transparent electrodes. The Raman results are useful for mechanistic diagnosis and for investigating the vibrational and electronic properties of the species under study. 

A related technique is based on the fact that signals from adsorbed species are much larger than from the same species in solution (surface enhanced Raman spectroscopy, SERS)23,24. The phenomenon was first noted in a study of the adsorption of pyridine on silver electrodes25, and has been extended to the investigation of the adsorption of many species such as, for example, porphyrins. 

Raman and infrared vibrations are mutually exclusive and consequently use of both techniques is required in order to obtain a set of vibrational bands for a molecule. The advent of powerful computer-controlled instrumentation has greatly enhanced the sensitivity of these vibrational spectroscopies by the use of Fourier transform (FT) techniques, whereby spectra are recorded at all frequencies simultaneously in the time domain and then Fourier transformed to give conventional plots of absorbance versus frequency. The wide range of applications of FT Raman spectroscopy is discussed by Almond et al. (1990). Specific examples of its use in metal speciation are the observation of the Co-C stretch at 500 cm-1 in methylcobalamin and the shift to lower frequency of the corrin vibrations when cyanide is replaced by the heavier adenosyl in going from cyanocobalamin to adenosylcobalamin (Nie et al., 1990). 

Nevertheless there exist strong covalent interactions in vitro between MYKO 63 and its relatives and DNA. However, the Scatchard technique does not give the actual sites the drug will graft on. In other words, we had to look for a more local technique which would allow to reach the location in DNA of these sites. Raman spectroscopy was chosen for this purpose because it had previously proved successful for studying in this way interactions of many biological systems with nucleosides or DNA 

During flash photolysis of either gaseous CFjl or gaseous CH3I, Kasper and Pimentel 184) observed laser action at 1.30 pm, due to the Fi/2 / 3/2 transition of atomic iodine. The high gain obtained 

These examples should have illustrated the importance of lasers as powerful tools in elucidating many details of photochemical processes which are not accessible with conventional light sources. 

It is certainly no exaggeration to say that the application of lasers in Raman spectroscopy has revolutionized this field, giving new impetus to many investigations and opening up new areas of research. There are several reasons why lasers are in many cases superior to conventional lamps. 

The small linewidths of exciting laser lines result in Raman spectra with considerably improved resolution 185a) Brandmiiller et al. 186) 

The small laser beam diameter, its low divergence and the possibility of focusing the beam onto an area of less than 10 cm allows small samples to be used. Schrader and Meier recorded, for instance, Raman spectra from 5 ul of acetyl-a-oxypropionitrile and from 5 pi CCI4. 

Gas-phase studies where relevant tautomeric compounds are described are ihore scarce, but include uracil, thymine, and adenine [97CPL(269)39]. In the case of the 2-pyridone/hydroxypyridine equilibrium, the intensity of the OH and NH stretching vibrations was measured for eight temperatures in the range from 428 to 533 K in the gas phase. This allows determination otAH and AS for the equilibrium (92JPC1562). 

Other advances in the use of IR spectroscopy are (1) The substitution of sulfur by selenium, for comparison with the spectra of benzimidazole-, benzoxazole-, and benzothiazole-2-thiones 72 (80AJC279). (2) The use of IR, as a quantitative tool to determine the association (homo- and heterodimers) of thia- and oxa-diazolin-5-thiones and -5-ones 73 (80NJC527). 

The authors claim that these associations, which are destroyed in fixed compounds, play an important role in the calculation of Ty.The cases of 1,2,4-triazole-5-thiones 74 [97SA(A)699] and of pyridone dimers 15a-15a and 15a-15b were also studied [96MI(13)65]. (3) The recording of IR spectra in solution at different temperatures to determine the effect of the temperature on Kj-, for instance, in pyrazolinones [83JPR(325)238] and in cytosine-guanine base pairs [92MI(9)881]. (4) The determination of the equilibrium 2-aminopyridine/acetic acid 2-aminopyridinium acetate (see Section III.E) in the acid-base complex was carried out by IR (97NKK100). 

The discussion above relating to the vibrational frequencies of molecules implied that all vibrational modes are capable of absorbing infrared 

It is important to appreciate that Raman shifts are, in theory, independent of the wavelength of the incident beam, and only depend on the nature of the sample, although other factors (such as the absorbance of the sample) might make some frequencies more useful than others in certain circumstances. For many materials, the Raman and infrared spectra can often contain the same information, but there are a significant number of cases, in which infrared inactive vibrational modes are important, where the Raman spectrum contains complementary information. One big advantage of Raman spectroscopy is that water is not Raman active, and is, therefore, transparent in Raman spectra (unlike in infrared spectroscopy, where water absorption often dominates the spectrum). This means that aqueous samples can be investigated by Raman spectroscopy. 

An alternative to univariate calibration is to use multivariate techniques to sense when a steady state has been reached in a chemical reaction. This approach has been successfully apphed to the detection of reaction end points [82]. A very similar technique can be used to establish deviation from steady state in a continuous process reactor. 

LEDs - relatively weak sources, but extremely small  

optical parametric oscillators (OPOs) - a powerful solid-state source of broadly tuneable coherent radiation  

quantum cascade lasers (QCLs) - a novel type of semiconductor laser [86]. 

Both infrared and Raman spectra are concerned with measuring molecular vibration and rotational energy changes. However, the selection rules for Raman spectroscopy are very different from those of infrared - a change of polarisability 

7This is in accord with the spectroscopic selection rules, derived from theoretical arguments, that predict which transitions between rotational and vibrational energy levels are allowed and which are forbidden.  

Exercise 9-13 Carbon dioxide gives two infrared absorption bands but only one Raman line. This Raman line corresponds to a different vibration than the infrared absorptions. Decide which vibrational modes are infrared active (i.e., make the molecule electrically unsymmetrical during at least part of the vibration) and which is Raman active (i.e., occurs so the molecule is electrically symmetrical at all times during the vibration, see Section 9-7A). 

The reverse process may also take place. If the collision with a photon brings a 

Inelastic scattering of light due to the excitation of vibrations had already been predicted in 1923 [37] and was confirmed experimentally a few years later by Raman [38], Because at that time the Raman effect was much easier to measure than infrared absorption, Raman spectroscopy dominated the field of molecular structure determination until commercial infrared spectrometers became available in the 1940s [10]. 

As in infrared spectroscopy, not all vibrations are observable. A vibration is Raman active if it changes the polarizability of the molecule. This requires in general that the molecule changes its shape. For example, the vibration of a hypothetical spherical molecule between the extremes of a disk-shaped and a cigar-shaped ellipsoid would be Raman active. We recall that the selection rule for infrared spectroscopy was that a dipole moment must change during the vibration. As a consequence the stretch vibrations of for example H2 (4160.2 cm 1), N2 (2330.7 cm-1) and 02 (1554.7 cm 1) are observed in Raman spectroscopy but not in infrared. The two techniques thus complement each other, in particular for highly symmetrical molecules. 

A strong point of Raman spectroscopy for research in catalysis is that the technique is highly suitable for in situ studies. The spectra of adsorbed species interfere weakly with signals from the gas phase, enabling studies under reaction conditions to be performed. A second advantage is that typical supports such as silica and alumina are weak Raman scatterers, with the consequence that adsorbed species can be measured at frequencies as low as 50 cm-1. This makes Raman 

An interesting and powerful new development in Raman spectroscopy of catalysts is the use of a UV laser to excite the sample. This has two major advantages. First, the scattering cross section, which varies with the fourth power of the frequency, is substantially increased. Second, the Raman peaks shift out of the visible region of the spectrum where fluorescence occurs. The reader is referred to Li and Stair for applications of UV Raman spectroscopy on catalysts [40]. 

1) The stress distribution in diamond film is basically compressive, and rapidly decreases at 10-15pm away from the diamond/Si interface. 

2) Near the interface, a biaxial stress exists in the diamond film, while near the growth surface, the stress tensor is more complicated. 

3) Grain boundaries are the major source of the intrinsic stress. 

The change in the depth causes the change in the band intensities but not in the band peak positions. The corresponding compressive stresses were evaluated to be 0, 1.7, and 5.3 GPa, respectively. 

8) From the Raman band width, it is evaluated that the standard deviation of the stress is 2 GPa, which is five times greater than the mean stress. 

Conducting polymer can be reversibly switched between the first three states at the electrochemical potentials shown (the exact potential depends on the nature 

FIGURE 1.33 Raman spectrum of PPy/pTS held at 0.8 V (versus Ag/AgCl) in 1 M NaCl with a pH of 2.25. (From T. Lewis, PhD thesis, University of Wollongong, 1998.) 

Another signal at about 1100 cm that can be assigned to sp -hybridized carbon appears upon excitation in the UV. It is termed T-band and results from a resonance amplification of o-states in amorphous tetrahedral carbon. In many cases, the portion of the latter is not very big, and so the intensity of the respective shoulder is rather low. This band originates from the shell of the individual particles where sp - and sp -hybridized carbon partially exist side by side. 

The sp -hybridized constituents of the nanodiamond sample (mostly the outer layers of the particles and, in parts, the material in the interstices of the agglomerates under examination) are characterized by two bands that have already been mentioned in the carbon nanotubes and onions the G- and the D-band. The exact position of the G-band (observed at about 1580 cm ) depends on both the excitation wavelength (dispersion) and the particle size. With decreasing wavelength of 

A very informative picture of the respective nanodiamond s structure can be obtained from summarizing the observed signals (diamond peak, G-band, D-band, T-band) and the bands of functional groups. In doing so, however, one must be aware that for particles bearing unordered graphitic material in their shell, the 

Hans-Ulrich Gremlich, Novartis AG, Basel. Switzerland 

As an alternative to infrared spectroscopy. Raman spectroscopy can be easier to use in some cases for example, whereas water and glass are strong infrared absorbers they are weak Raman scatterers, so that it is easy to produce a good-quality Raman spectrum of an aqueous sample in a glass container. 

The band at 1193cm is sensitive not only to the structural adjustment of the C-O-C backbone but also to the structural order of the CH3 group in the crystalline phase. From the analysis of the difference spectra and 2D correlation spectra in the 1500-1000 cm region, it is shown that the structural adjustment of the CH3 group unambiguously precedes that of the ester group [49]. 

For polymorphic polymers, such as PLLA, the characteristic FTIR bands can be correlated to the different crystal modifications and typically stay distinguishable in a certain 

The Raman spectra of PLA polymers are also characterized by a C=0 stretching region. The C=0 stretching mode in PLLA presents four active modes in the Raman region designated by A, B, Ej, and E2, which could be observed at 1749,1763,1769, and 1773 cm as mentioned in Table 8.1. The PDLA Raman spectrum is characterized by broad and asymmetric lines. Two bands at 1769 and 1749 cm  

TABLE 8.2 Assignments for the FTIR Bands in the 1260-1000 cm Region for PLLA a - and a-Crystals [52] 

FIGURE 8.8 FTIR spectra (a) and corresponding second derivatives (b) in the frequency region 1260-1000 cm recorded for the normal PLLA118 a-crystal and annealed (at 150°C for various periods (ta/min)) PLLAl 18 a -crystals. Adapted from Ref. 52 with permission from American Chemical Society. 

For a given intermediate state n , the first and second right-hand terms in Eq. 10.26 correspond to the first and second time-ordered graphs in Fig. 10.12, respectively. When a i a 2, the scattered radiation frequency CO2 is said to be 

Stokes-shifted from the incident frequency coi, anti-Stokes scattering is obtained when o)i 0)2- The energy difference h(co2 — ( i) normally matches either a molecular vibrational-rotational or rotational level difference, and the incident frequency cOi is usually some readily generated visible frequency (e.g., an Ar or He/Ne laser line) in conventional Raman spectroscopy. In such cases c 2 — 1- We may specialize Eq. 10.26 to chemical applications of 

Raman spectroscopy [1] by using Born-Oppenheimer states for the molecular zeroth-order states, 

This implies that the initial and final states k and m are different vibrational levels within the same (normally the ground) electronic state, and that the intermediate states n , in terms of which the virtual states are expanded, are vibrational levels in electronically excited manifolds (Fig. 10.13). Using this notation, the Raman transition amplitude becomes 

The polarizability tensor a(a ) for a molecule in electronic state 0 subjected to a sinusoidal electric field with circular frequency co has components 

Near-held microscopy makes use of a radiahon source that is subwavelength in size, and often formed from a tapered light tube with a subwavelength-sized aperture at the narrow end. The tip must approach the sample to within the dimension of the aperture (i.e. sub-micrometer), requiring accurate z-axis control. The efihciency of transmission through the aperture can be extremely poor (10 for A,/10) and thus one requires an intense light source such as laser- or synchrotron-generated IR. 

A tunable CO2 laser has been combined with an atomic-force-microscopy (AFM) microscope to form an apertureless near-held-imaging system [17]. This technique can produce spahal resoluhon of up to A/lOO with high throughput however, the tunable range of the CO2 laser is hmited to a region of the IR spectrum that is not parhcularly informahve for most IR chromophores (2300 cm ). 

Raman spectroscopy is a complementary technique to IR. Both IR and Raman spectra arise from the vibrahonal energy levels of the molecules. The difference in the informahon content of the two vibrahonal methods arises from differences in selechon rules. In the simplest terms, IR absorphon arises from vibrahonal modes that give rise to changes in the dipole moments of the bonds and consequenhy is most sensihve to polar bonds. Raman absorphon arises from changes in the induced polarity of bonds and is most sensihve to nonpolar bonds. For polymers, IR absorphon is sensitive to subshtutents on the backbone of the chain, i.e. C— H, C=0, C—OH, etc., whereas Raman absorphon is sensihve to the C—C backbone 

In normal Raman scattering, a molecule is excited to a virtual state, which corresponds to a quantum level related to the electron-cloud distortion created by the electric field of the incident light. A virtual state does not correspond to a real eigenstate (vibrational or electronic energy level) of the molecule, but rather is a sum over all eigenstates of the molecule. 

Raman scattering is envisaged as the process of reirradiation of scattered light by dipoles induced in the molecules by the incident light and modulated by the vibrations of the molecules. In normal Raman scattering by molecules in isotropic media, the dipoles are simply those which result from the action of the electric-field component E of the incident light on the molecules. 

Core shell ionization of an atom can have a variety of consequences. As it will be discussed in Sec. 4, the energy liberated when the hole that was left behind is filled by 

X-ray absorption spectrum of PCAT film on iron substrate 

The desire to obtain X-ray adsorption spectra from small features on chemically heterogeneous samples has also lead to the development of In this 

Depending on the orientation of the light wave and the molecule, an intense light wave can polarize the electron shells of a molecule and create a temporary dipole moment. Let there be a 3 x 3 polarizability tensor [a], which satisfies a relation with the components of the electric field of the light as [Ex, Ey, E ] to induce dipole components [ Uind-x Find-y Eind-zl which can then couple with one or more vibrations. Here it is sufficient to note that the electric field of a light wave can actually induce temporary dipole components in a molecule with a zero dipole moment and that can lead to 

You can teU from the double index on the elements of [a] such as a. that this is a second-order effect and generally depends on a more intense light source. 

FIGURE 12.23 CCLj Raman spectrum excited by 4358 Angstrom light from a Hg arc. (From Tobias, R. S., J. Chem. Ed., 44, 2, 1967. With permission of The Journal of Chemical Education.) 

Boltzmann probability of the sample molecule being in a higher energy state is less prior to the electronic excitation. If the corresponding Stokes line is already weak, it may be very difficult to observe the anti-Stokes lines. The spectmm here is from older technology, which used a Hg arc lamp for excitation before powerful lasers were available. 

This chapter introduces the student to the method of seeking a solution to a differential equation in the form of a polynomial, which was probably the method used by Schrodinger in 1926 to solve this problem in terms of Hermite polynomials. An undergraduate with two semesters of calculus should be able to follow this key derivation with pencil and paper, assuming enough time and patience are available, but we still provide most of the detailed calculus steps here. For students with only one semester of calculus, it would be better for the teacher to show the steps on the board in lecture. 

This is a powerful, highly sensitive, and nondestructive technique that provides structural information relative to the laser path inside the materials. It can be 

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Due to the very high intensity of the laser beams and their coherent nature they may be used in a variety of ways where controlled energy is required. Lasers are used commercially for excitation with a specific energy, e.g. in Raman spectroscopy or isotope separation. 

The varying actual orientation of molecules adsorbed at an aqueous solution-CCU interface with decreasing A has been followed by resonance Raman spectroscopy using polarized light [130]. The effect of pressure has been studied for fatty alcohols at the water-hexane [131] and water-paraffin oil [132] interfaces. 

RS Raman spectroscopy [210, 211] Scattered monochromatic visible light shows frequency shifts corresponding to vibrational states of surface material Can observe IR-forbidden absorptions low sensitivity... 

RRS Resonance Raman spectroscopy [212, 213] Incident light is of wave length corresponding to an absorption band Enhanced sensitivity... 

SERS Surface-enhanced Raman spectroscopy [214-217] Same as RS but with roughened metal (usually silver) substrate Greatly enhanced intensity... 

See Refs. 80 and 81 for other examples. Surface-enhanced Raman spectroscopy is discussed in Section XVI-4C. 

SERS. A phenomenon that certainly involves the adsorbent-adsorbate interaction is that of surface-enhanced resonance Raman spectroscopy, or SERS. The basic observation is that for pyridine adsorbed on surface-roughened silver, there is an amazing enhancement of the resonance Raman intensity (see Refs. 124—128). More recent work has involved other adsorbates and colloidal... 

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

Wliat does one actually observe in the experunental spectrum, when the levels are characterized by the set of quantum numbers n. Mj ) for the nonnal modes The most obvious spectral observation is simply the set of energies of the levels another important observable quantity is the intensities. The latter depend very sensitively on the type of probe of the molecule used to obtain the spectmm for example, the intensities in absorption spectroscopy are in general far different from those in Raman spectroscopy. From now on we will focus on the energy levels of the spectmm, although the intensities most certainly carry much additional infonnation about the molecule, and are extremely interesting from the point of view of theoretical dynamics. 

Because of the two frequencies, Wj and Wg, that enter into the Raman spectrum, Raman spectroscopy may be thought of as a two-dimensional fomi of spectroscopy. Nomially, one fixes oij and looks at the intensity as a frmction of tOj, however, one may vary tOj and probe the intensity as a frmction of tOj - tOg. This is called a Raman excitation profile. 

As described at the end of section Al.6.1. in nonlinear spectroscopy a polarization is created in the material which depends in a nonlinear way on the strength of the electric field. As we shall now see, the microscopic description of this nonlinear polarization involves multiple interactions of the material with the electric field. The multiple interactions in principle contain infomiation on both the ground electronic state and excited electronic state dynamics, and for a molecule in the presence of solvent, infomiation on the molecule-solvent interactions. Excellent general introductions to nonlinear spectroscopy may be found in [35, 36 and 37]. Raman spectroscopy, described at the end of the previous section, is also a nonlinear spectroscopy, in the sense that it involves more than one interaction of light with the material, but it is a pathological example since the second interaction is tlirough spontaneous emission and therefore not proportional to a driving field... 

COHERENT ANTI-STOKES RAMAN SPECTROSCOPY (CARS)... 

Our first example of aP - signal is coherent anti-Stokes Raman spectroscopy, or CARS. Fomially, tire emission signal into direction k= - k + k. has 48 Feynman diagrams that contribute. Flowever, if the... 

Myers A B and Mathies R A 1987 Resonance Raman intensities A probe of excited-state structure and dynamics Biological Applications of Raman Spectroscopy yo 2, ed T G Spiro (New York Wiley-Interscience) pp 1-58... 

Knopp G, Pinkas I and Prior Y 2000 Two-dimensional time-delayed coherent anti-Stokes Raman spectroscopy and wavepacket dynamics of high ground-state vibrations J. Raman Spectrosc. 31 51... 

Vibrational spectroscopy provides detailed infonnation on both structure and dynamics of molecular species. Infrared (IR) and Raman spectroscopy are the most connnonly used methods, and will be covered in detail in this chapter. There exist other methods to obtain vibrational spectra, but those are somewhat more specialized and used less often. They are discussed in other chapters, and include inelastic neutron scattering (INS), helium atom scattering, electron energy loss spectroscopy (EELS), photoelectron spectroscopy, among others. 

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. 

One of the well known advantages of resonance Raman spectroscopy is that samples dissolved in water can be studied since water is transparent in the visible region. Furthennore, many molecules of biophysical interest assume their native state in water. For this reason, resonance Raman spectroscopy has been particularly strongly embraced in the biophysical connnunity. 

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... 

The advantages of resonance Raman spectroscopy have already been discussed in section BL2.2.3. For these reasons it is rapidly becoming the method of choice for studying large molecules in solution. Flere we will present one study that exemplifies its attributes. There are two complementary methods for studying proteins. 

Figure Bl.2.11. Biologically active centre in myoglobin or one of the subunits of haemoglobin. The bound CO molecule as well as the proximal and distal histidines are shown m addition to the protohaeme unit. From Rousseau D L and Friedman J M 1988 Biological Applications of Raman Spectroscopy vol 3, ed T G Spiro (New York Wiley). Reprinted by pennission of John Wiley and Sons Inc.

Time-resolved spectroscopy has become an important field from x-rays to the far-IR. Both IR and Raman spectroscopies have been adapted to time-resolved studies. There have been a large number of studies using time-resolved Raman [39], time-resolved resonance Raman [7] and higher order two-dimensional Raman spectroscopy (which can provide coupling infonuation analogous to two-dimensional NMR studies) [40]. Time-resolved IR has probed neutrals and ions in solution [41, 42], gas phase kmetics [42] and vibrational dynamics of molecules chemisorbed and physisorbed to surfaces [44]- Since vibrational frequencies are very sensitive to the chemical enviromnent, pump-probe studies with IR probe pulses allow stmctiiral changes to... 

Raman microscopy is more developed than its IR counterpart. There are several reasons for this. First, the diffraction limit for focusing a visible beam is about 10 times smaller than an IR beam. Second, Raman spectroscopy can be done in a backscattering geometry, whereas IR is best done in transmission. A microscope is most easily adapted to a backscattermg geometry, but it is possible to do it in transmission. 

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