Laser Raman spectroscopy, molecular

Laser-Raman spectroscopy Molecular bond directions can be specific to crystalline or non-crystalline regions, parts of structure cos 0, cos 0, cos Ocos , etc. (hyper-Raman might give higher moments) To relate polarisability changes to directions in molecules may not be as straightforward as assuming a bond direction correspondence Transparent specimens, with little or no fluorescence required... 

Chemical Properties. MSA combines high acid strength with low molecular weight. Its pK (laser Raman spectroscopy) is —1.9, about twice the acid strength of HCl and half the strength of sulfuric acid. MSA finds use as catalyst for esterification, alkylation, and in the polymerisation and curing of coatings (402,404,405). The anhydrous acid is also usefijl as a solvent. 

The vibrations of molecular bonds provide insight into bonding and stmcture. This information can be obtained by infrared spectroscopy (IRS), laser Raman spectroscopy, or electron energy loss spectroscopy (EELS). IRS and EELS have provided a wealth of data about the stmcture of catalysts and the bonding of adsorbates. IRS has also been used under reaction conditions to follow the dynamics of adsorbed reactants, intermediates, and products. Raman spectroscopy has provided exciting information about the precursors involved in the synthesis of catalysts and the stmcture of adsorbates present on catalyst and electrode surfaces. 

Laser Raman spectroscopy, 24 293-341 see also Raman spectroscopy molecular precursors for tailored metal catalysts, 38 298... 

It may be concluded, from the analysis of the Raman results, that the information provided by Raman spectroscopy is, in essence, similar to that of infrared spectroscopy. The exploitation of the data, namely, the frequencies and intensities due to the molecular vibrations, is of a certain benefit in giving some insight as to the conformations of carbohydrates, and their interactions with the environment. As laser-Raman spectroscopy is applicable to solids, as well as to aqueous solutions, the linear relationship between Raman intensities and mass concentrations, and the specificity and high quality of the spectra experimentally obtained, make this technique particularly promising in investigations of the chemistry and biochemistry of carbohydrates. 

Laser Raman spectroscopy has played a major role in the study of electrochemical systems (see Section 3.4). The technique provides molecular-specific information on the structure of the solid-solution interfaces in situ and is particularly suited for spectroelectrochemical studies of corrosion and surface film formation. Metals such as Pb, Ag, Fe, Ni, Co, Cu, Cr, Ti, Au and Sn, stainless steel and other alloys in various solutions have been studied by the technique. 

Bradley EB, Frenzel CA. 1970. On the exploitation of laser Raman spectroscopy for the detection and identification of molecular water pollutants. Water Res 4 124-128. 

Laser Raman spectroscopy has been used as a tool to elucidate the molecular structure of crystals, liquids, and amorphous alloys in the As-S-Se-Te system. Characteristic monomer and polymer structures have been identified, and their relative abundances have been estimated as a function of temperature and atomic composition. These spectroscopic estimates are supported by calculations based on the equilibrium polymerization theories of Tobolsky and Eisenberg (1,2) and of Tobolsky and Owen (3). Correlations between the molecular structure of the amorphous alloys and physicochemical properties such as the electron drift mobility and the glass transition temperature are presented. 

In summary, laser Raman spectroscopy is useful for investigating the molecular microstructure of amorphous materials especially when reinforced by theoretical calculations. Correlations between spectroscopic data and the results of other physicochemical measurements are established. A detailed evaluation of the implications of these correlations must, however, be omitted to avoid intrusion upon areas of proprietary interest. 

The formation of prenuclear molecular aggregates or embryos in a supersaturated solution can be studied by various physical methods, such as laser Raman spectroscopy [23], a technique that is especially... 

In general, Raman spectroscopy has been used very little, if at all, to perform quantitative analyses its primary use has been in the study of molecular structure. However, one possible use of laser Raman spectroscopy for quantitative purposes is the identification and determination of trace levels of molecular pollutants in water [10]. The Raman spectrum of distilled water is weak and uncomplicated thus it is possible to detect and distinguish Raman bands of pollutants in natural waters. For example, it is possible to detect as little as 50 ppm of benzene in distilled water using only 5 mW of laser power from a He-Ne gas laser at 6328 A. With improved excitation techniques and 50 mW laser power, it should be possible to detect certain Raman-active pollutants at less than 5 ppm levels. 

Molecular Characterization of Dieiectric Fiims by Laser Raman Spectroscopy... 

The primary object of Raman spectroscopy is the determination of molecular energy levels and transition probabilities connected with molecular transitions that are not accessible to infrared spectroscopy. Linear laser Raman spectroscopy, CARS, and hyper-Raman scattering have very successfully collected many spectroscopic data that could not have been obtained with other techniques. Besides these basic applications to molecular spectroscopy there are, however, a number of scientific and technical applications of Raman spectroscopy to other fields, which have become feasible with the new methods discussed in the previous sections. We can give only a few examples. 

Polymerisation of vinyl toluene in quaternary microemulsions containing cetyltrimethylammonium bromide as the cationic surfactant was studied using laser Raman spectroscopy and dilatometry. The influences of water soluble (potassium peroxodisulphate, ammonium peroxodisulphate) and oil-soluble (azobisisobutyronitrile, benzoyl peroxide) initiators, monomer, surfactant, cosurfactants (n-alcohol and bifunctional alcohols) and temperature on the rates of polymerisation, energy of activation, particle diameter, number of polymer particles, molecular weight of polyvinyl toluene and number of polymer chains per latex particle were investigated. The dependencies of the kinetic and latex size parameters on the initiators and co-surfactants are discussed in terms of the efficiency of the initiators in initiating the polymerisation and on the interfacial partitioning behaviour of various co-surfactants. 19 refs. 

One example is intracavity Raman spectroscopy of molecules in a supersonic jet, demonstrated by van Helvoort et al. [8.36]. If the intracavity beam waist of an argon-ion laser is shifted to different locations of the molecular jet (Fig. 8.10), the vibrational and rotational temperatures of the molecules (Sect. 9.2) and their local variations can be derived from the Raman spectra. More details of recent techniques in linear laser Raman spectroscopy can be found in [8.11,8.37]. 

J Purvis, DI Bower. Molecular orientation in poly(ethylene terephthalate) by means of laser-Raman spectroscopy. J Polym Sci Poly Phys Ed 14 1461-1484, 1976. 

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