Raman spectroscopy, general discussion

The Raman effect by Neil Everett, Bert King and Ian Clegg in Chemistry in Britain, July 2000, p. 40, is a good general introduction, written for scientists with no prior experience of Raman spectroscopy. Each of the books cited above under general reading discuss Raman spectroscopy, but in greater depth. 

The subsequent reaction of bromine treated NaX and CsX with benzene revealed two types of behavior (35). At saturation Br2 coverage surface donor complexes were formed on sites III and II, whereas at less than Br2 saturation (only site II occupied) benzene reacted rapidly to form addition products containing carbon-bromine bonds. The unique ability to use Raman spectroscopy in general for obtaining low frequency spectral data in studies of in situ catalytic process was discussed by the authors. 

This chapter discusses the use of Raman spectroscopy for analysis of biofluids, specifically blood and urine. After a brief overview of the clinical motivations for analyzing biofluids, the benefits of optical approaches in general and Raman spectroscopy in particular are presented. The core of the chapter is a survey of equipment, data-processing, and calibration options for extracting concentration values from Raman spectra of biofluids or, in the in vivo cases, volumes that include biofluids. The chapter finishes with a discussion of fundamental limits on how accurately concentrations can be determined from Raman measurements and how closely current experiments approach that limit. 

A general discussion regarding the instrumentation which can be used for the measurement of CD spectroscopy has been provided by Donald Bobbitt, while the more specialized requirements associated with vibrational optical activity have been discussed by Laurence Nafie. This latter chapter deals with both the methods of vibrational CD spectroscopy as well as raman vibrational optical activity. The use of CD as a detector in liquid chromatography represents an important area of heightened activity, and this has been covered by Andras Gergely. 

Let us first briefly discuss spontaneous nonlinear Raman spectroscopy on an isolated single molecule. Generally the induced dipole moment p in a molecular system is written in the form... 

Joint interpretation of the IR and Raman spectra of biomolecules, which frequently lack symmetry properties, may afford more extensive information concerning the primary, secondary and tertiary structure, than does the interpretation of one type of spectrum only. Many systems can only be investigated in aqueous solution, a good solvent for Raman spectroscopy. The technique of resonance Raman spectroscopy facilitates investigations of pigments and the NIR FT Raman spectroscopy allows the investigation of nearly all samples which has not been possible before due to absorption and fluorescence. Spectra of biomolecules are exhaustively discussed in Sec. 4.7. Here only some general features are discussed. 

This section discusses applications of IR and Raman spectroscopy to materials with reasonable or even very high conductivity. These systems generally present special problems in addition to those described in earlier sections. Incident radiation interacts not only with the vibrational excitations of the material but also with the free carriers and with its electronic structure. These interactions may create phenomena such as free carrier absorption, excitation across the energy gap, exciton transitions, or light scattering by free electrons. Excitations are very often in the IR spectral range, particularly in the... 

Folydlacetylenes offer a unique opportunity of studying structure/property relationships in polymers. This paper is concerned with structural factors which control mechanical properties. The effect of the size of side-groups upon the Young s moduli of different polydiacetylenes is discussed briefly. The effect of internal and surface defects upon the strengths of individual fibres is also described. Examples are given of how Raman spectroscopy can be used to follow the deformation of fibres and it is shown how this can be extended to fibres in composites. The general mechanical properties of the composites are also described. 

Diatomic cations, neutral molecules, and anions represent the type of inorganic species which has been most extensively studied by resonance Raman spectroscopy. Iodine in the gaseous, dissolved, and matrix-isolated states has been the subject of particularly detailed studies, and it is this molecule for which the greatest number of members (25) of a resonance Raman progression has so far been observed (66). The relation between resonance Raman and resonance fluorescence spectra has been discussed in Section 2, but it is worth illustrating the general principles involved by reference to the work on iodine. 

Sampling techniques for Raman spectroscopy are relatively general, since the only requirement is that the monochromatic laser beam irradiate the sample of interest and the scattered radiation be focused on the detector. The sampling discussion outlined here is applicable to both types of spectrometers (dispersive/ FT). 

There is a tendency in discussing a new technique to point out its advantages and that is the approach taken here for laser Raman spectroscopy. It is worth emphasizing that fluorescence still presents a major sampling problem for most commercial materials in the Raman and that at this time infrared is much more widely applicable to applied polymer science. Infrared is generally the more effective tool for trace analyses and for quantitative data. 

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