Raman spectroscopy types

The research in this area builds on the earlier work of Haka et al. [57] who found that excised calcifications can be classified into two groups using Raman spectroscopy type I - calcium oxalate dihydrate (cod) and type II - calcium hydroxyapatite (hap). Calcium oxalate crystals are mainly found in benign ductal cysts while calcium hydroxyapatite is found in both carcinoma and in benign breast tissue the chemical specificity of Raman spectroscopy identifies... 

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. 

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. 

The planar structure of thiazole (159) implies for the molecule a Cj-type symmetry (Fig. 1-8) and means that all the 18 fundamental vibrations are active in infrared and in Raman spectroscopy. Table 1-22 lists the predictions made on the basis of this symmetry for thiazole. 

Normal modes of vibration, with their corresponding normal coordinates, are very satisfactory in describing the low-lying vibrational levels, usually those with u = 1 or 2, which can be investigated by traditional infrared absorption or Raman spectroscopy. For certain types of vibration, particularly stretching vibrations involving more than one symmetrically equivalent terminal atom, this description becomes less satisfactory as v increases. 

From 1960 onwards, fhe increasing availabilify of intense, monochromatic laser sources provided a fremendous impetus to a wide range of spectroscopic investigations. The most immediately obvious application of early, essentially non-tunable, lasers was to all types of Raman spectroscopy in the gas, liquid or solid phase. The experimental techniques. 

In aqueous solution, all the sodium peroxoborates dissociate for the most part into boric acid, or its anion, and hydrogen peroxide. Peroxoborate species are also present in these solutions, depending on the pH and the concentration for the species type. The nature of these species has been extensively examined by classical physicochemical methods (13), by nmr, and by Raman spectroscopy (14—17). Both monomeric and polymeric species are usually present. There is some evidence (18) suggesting that these peroxoborates are more reactive than hydrogen peroxide alone under similar conditions. 

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

Raman spectroscopy is sensitive to ordering arrangements of crystal structures, the effect depending on the type of order. Ordering atoms onto specific lattice sites in... 

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

There are, at present, two overriding reasons an experimentalist would choose to employ laser Raman spectroscopy as a means of studying adsorbed molecules on oxide surfaces. Firstly, the weakness of the typical oxide spectrum permits the adsorbate spectrum to be obtained over the complete fundamental vibrational region (200 to 4000 cm-1). Secondly, the technique of laser Raman spectroscopy is an inherently sensitive method for studying the vibrations of symmetrical molecules. In the following sections, we will discuss spectra of pyridine on silica and other surfaces to illustrate an application of the first type and spectra of various symmetrical adsorbate molecules to illustrate the second. 

Pure pigments and dyes can be identified from their IR spectrum. Some reference spectra are given in the Hummel and Scholl collection [9]. Other than simple white pigments or solvent soluble types, identification of pigments in finished products is particularly difficult. Raman spectroscopy can aid the positive identification of pigments such as titanium dioxide. 

The molecular structure of Li-, Na-, and K-silicates in 0.2 to 3 mole SiOj/L aqueous solutions has been investigated by FTIR and Raman spectroscopy to help exploring their solidification process. These silicates were found to be only partially dissociated and their average molecular weight (AMW) varies with the type of the alkaline ion, the alkaline/silicon ratio, and the concentration. It is demonstrated that these differences are associated with differences in the Qn connectivity ratios of [Si04] tetrahedra and in the dominating siloxane ring structures which can be identified by their vibrational spectra. 

Under the synthesis conditions in this study, gels with the organic templates, viz., MCHA, TEA, TPA, and TEAOH form clearly the AlP04-5 structure. The type of the organic template used affects the morphology of the produced crystals due to the different ways of interaction between the template and the host framework, which could be investigated using FT-Raman spectroscopy. 

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