Raman spectroscopic techniques

Raman and infrared spectroscopy both excite vibrational states, but by different mechanisms. Vibrating molecules generate changes in the polaris-ability and/or in the magnitude of the dipole associated with the molecule. These changes give rise to the spectroscopic effects of Raman (inelastic) scattering and infrared absorption, respectively, which are the two most valuable techniques available for the measurement of the vibrational and rotational characteristics of molecules. 

Not surprisingly, therefore, modern RS relies on the availability of lasers as intense and stable light sources. 

All materials possess polarisability , i.e. if placed in an oscillating electric field of magnitude E (Vm ) an electric dipole /u will be induced. The proportionality constant or polarisability a (a tensor quantity) in 

The Raman cross-section is proportional to v and to a. The molecular cross-section of Raman spectroscopy is some ten orders of magnitude smaller than that of IR spectroscopy. However, for a typical classical detector of Raman spectra, the photomultiplier (PMT), the number of photons to produce the noise equivalent power (NEP), which is the light flux necessary to produce a signal of the same magnitude as the noise, is up to ten orders of magnitude smaller than those of detectors employed 

The Raman sampling technique is considerably easier than for IR and the information supplied can be more significant. Whereas IR requires use of thin film samples (unless reflectance), a Raman cell can easily accommodate a bulk specimen, fibre, powder, film or solution with minimum sample thickness of the order of several mm, which can easily be heated or cooled, pressurised or irradiated, stretched or bent. 

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Cryogenic inorganic chemistry a review of metal-gas reactions as studied by matrix isolation infrared and Raman spectroscopic techniques, G. A. Ozin and A. Vander Voet, Prog. Inorg. Chem., 1975,19,105-172 (303). 

It is well known that vanadium can replace phosphorus or arsenic in the apatite lattice. Most of the orthovanadates which crystallize in this form have been investigated by IR and Raman spectroscopic techniques 62—64). The results of these studies are summarized in Table 4. The space group of all of these compounds is certainly C ft with the VO4 ion lying on a C site. Therefore, one should always find a nine band spectrum. Phosphorus apatites behave similarly, as seen in Ref. (65). 

IR AND Raman Spectroscopic Techniques in Studies of Flavonoid Structures... 

In this contribution we present the unique potential of the above-mentioned Raman spectroscopic techniques for viral and microbial studies in biomedical and pharmaceutical applications. 

Because of minimal sample preparation and minimally invasive approaches Raman spectroscopy has the potential to gain new insights into viral and microbial biochemistry as well as a rapid identification of pathogenic microorganisms. In this chapter the unique potential of several Raman spectroscopic techniques for medical and pharmaceutical issues is discussed, which focus on the analysis of viruses as well as on microbial detection... 

Moisturization in skin can be measured in a variety of ways, some of the more common of which are summarized in Table 31.3. It can be measured directly as an increase in hydration in skin or improvement in clinical and sensory symptoms resulting from the improved hydration state of skin. At the most basic level, consumer perceptions can provide a measure of skin feel and appearance but more often are used to quantify the sensory aspects that cannot be measured instrumentally.45 Expert clinical grading provides a more refined quantitative measure of appearance 46 The human eye is still the most powerful tool for discriminating subtle changes in appearance 47 However, bioinstrumentation is required to measure insensible parameters such as the hydration level in skin.48-50 While methods based on electrical properties of skin are widely used to indirectly measure water content, Near-Infra Red and Raman Spectroscopic techniques are more closely reflective of the actual hydration state.51,52... 

The initial dynamics of the photodissociations of methyl iodide29 in hexane and alkyl iodides30 in cyclohexane have been studied by resonance Raman spectroscopic techniques. The dominant motion during the first 10 fs after excitation involves stretching of the C—I bond. 

The interfacial region of a metal up to the IHP has been considered as an electronic molecular capacitor, and this model has explained many experimental results with success20. Another important model is the jellium model21 (Fig. 3.13fo). From an experimental point of view, the development of in situ infrared and Raman spectroscopic techniques (Chapter 12) to observe the structure, and the calculation of the bond strength at the electrode surface can better elucidate the organization of the double layer. Other surface analytical techniques such as EXAFS are also valuable. 

Williams, A. C., et al., A critical comparison of some Raman spectroscopic techniques for studies of human stratum comeum. Pharmaceutical Research 70(11) 1642-1647, 1993. 

Beginning in the mid-thirties, the IR and Raman spectroscopic techniques achieved major importance. Still later, neutron diffraction and nuclear magnetic resonance measurements became available to describe the positions of hydrogen atoms, thus providing a valuable supplement to x-ray studies. )... 

The present piece of work, in an effort to contribute in establishing a correlation between catalytic performance, catalyst structure and surfece composition, presents combined results of reactivity in activation of syn-gas (CO/H2) and CO2/H2 mbetures. Hydrogen chemisorption (HChS), TEM, and XPS and Raman spectroscopic techniques have also been used. 

Wackerbarth, H., Klar, U., Gunther, W., and Hildebrandt, P. (1999) Novel time-resolved surface-enhanced (resonance) Raman spectroscopic technique for smdying the dynamics of interfadal processes application to the electron transfer reaction of cytochrome c at a silver electrode. Applied Spectroscopy, 53, 283-291. 

The symmetry allowed modes at ft 0 have been determined using infrared and Raman spectroscopic techniques by Iqbal el al for a number of alkali pseudohalides 19, 41, 54,55), and ammonium 56), barium 26), a-lead 57) and thallous azide 45). The A 0 dependence of the first... 

Bartlett, McKee, and co-workers have investigated the XeF4-SbF6 system by X-roy crystallographic and Raman spectroscopic techniques. They were... 

As opposed to FTIR, Raman spectroscopic technique can detect totally symmetric vibrational modes and also nonpolar homonuclear bonds [120]. 

Real-time chemical processing and analysis yields improvement in product consistency and quality while maximising process efficiency. IR and Raman spectroscopic techniques can be used for the study of kinetics of copolymerisation and terpolymers. These... 

A comparison of standard Raman versus resonance Raman spectroscopic techniques. [Copyright Semrock, Inc., reproduced by permission from http //www.semrock.com/ultraviolet-uv-raman-spectroscopy.aspx (accessed December 21, 2013).]... 

Another polymer that has been investigated in several miscible polymer blends is polysulfone (PSF). Blends made from polyamide 11 (PAll) and sulfonated polysulfone (SPSF) were prepared by solution casting from dimethyl formamide (DMF) (Deimede et al. 2000b). In that work, differential scanning calorimetry (DSC) showed a melting point depression of the equilibrium melting point of the PAll. With lower degrees of sulfonation, less interaction between the two polymers was observed. FT-IR and FT-Raman spectroscopic techniques were used to confirm the nature of the specific interactions involved. 

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