Raman spectroscopy fundamentals

For a comprehensive overview of Raman spectroscopy fundamentals, theory, and applications, see (a) McCreery, R. L. in Chemical Analysis Vol 157, Wmefordner J. D, Ed. Wiley New York, 2000. (b) Lewis, I. R. Edwards, H. G. M. Handbook of Raman Spectroscopy, Erom the Research Laboratory to the Process Line Marcel Dekker New York, 2001. (c) Pivonka, D. E. Chalmers, J. M. Griffiths, R R. Eds. Applications of Vibrational Spectroscopy in Pharmaceutical Research and Development WUey New York, 2007. (d) Dollish, F. R. Fateley, W. G. Bentley, F. F. Characteristic Raman Frequencies of Organic Compounds Wiley New York, 1974. 

IR and Raman Spectroscopy Fundamental Processing. Siegfried Wartewig Copyright 2003 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30245-X... 

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. 

Infrared Spectrophotometry. The isotope effect on the vibrational spectmm of D2O makes infrared spectrophotometry the method of choice for deuterium analysis. It is as rapid as mass spectrometry, does not suffer from memory effects, and requites less expensive laboratory equipment. Measurement at either the O—H fundamental vibration at 2.94 p.m (O—H) or 3.82 p.m (O—D) can be used. This method is equally appticable to low concentrations of D2O in H2O, or the reverse (86,87). Absorption in the near infrared can also be used (88,89) and this procedure is particularly useful (see Infrared and raman spectroscopy Spectroscopy). The D/H ratio in the nonexchangeable positions in organic compounds can be determined by a combination of exchange and spectrophotometric methods (90). 

Band gaps in semiconductors can be investigated by other optical methods, such as photoluminescence, cathodoluminescence, photoluminescence excitation spectroscopy, absorption, spectral ellipsometry, photocurrent spectroscopy, and resonant Raman spectroscopy. Photoluminescence and cathodoluminescence involve an emission process and hence can be used to evaluate only features near the fundamental band gap. The other methods are related to the absorption process or its derivative (resonant Raman scattering). Most of these methods require cryogenic temperatures. 

Raman spectroscopy can in principle be applied to this problem in much the same manner as infrared spectroscopy. The primary difference is that the selection rules are not the same as for the infrared. In a number of molecules, frequencies have been assigned to combinations or overtones of the fundamental frequency of the... 

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. 

Vibrational spectroscopy and in particular Raman spectroscopy is by far the most useful spectroscopic technique to qualitatively characterize polysulfide samples. The fundamental vibrations of the polysulfide dianions with between 4 and 8 atoms have been calculated by Steudel and Schuster [96] using force constants derived partly from the vibrational spectra of NayS4 and (NH4)2Ss and partly from cydo-Sg. It turned out that not only species of differing molecular size but also rotational isomers like Ss of either Cy or Cs symmetry can be recognized from pronounced differences in their spectra. The latter two anions are present, for instance, in NaySg (Cs) and KySg (Cy), respectively (see Table 2). 

Raman spectroscopy works in the same spectral region as infrared spectroscopy but their physical principles and applicabihties are fundamentally different. Com-... 

Several methods are successfully applicable in this field, e.g. dielectric relaxation methods 164>, IR investigations in the near, fundamental, and far IR regions 165>, RAMAN spectroscopy 166>, NMR spectroscopy 32-34-16 ), and ultrasonic absorption i 8-i70). 

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. 

R.M. Patel, A.K. Doufas and R.R Raradkar, Raman spectroscopy for spinline crystallinity measurements. II. Validation of fundamental fiber-spinning models, J. Appl. Polym. Sci., 109, 3398-3412 (2008). 

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