Raman spectroscopy compared with infrared spectroscop

Vibrational spectroscopy with neutrons is a spectroscopic technique in which the neutron is used to probe the dynamics of atoms and molecules in solids. In this introductory chapter we provide a descriptive account of the discovery and properties of the neutron, the development of neutron scattering, how inelastic neutron scattering spectroscopy compares with infrared and Raman spectroscopy and the benefits of using the neutron as a spectroscopic probe. 

Unique applications employ both types of spectroscopies for structural analysis. The complementary nature of infrared and Raman effects can be seen in the structure determination of 1 1 hexafluoroisobutylene and vinylidene fluoride copolymer. This problem is virtually impossible to solve with other techniques. The two monomers can be linked in two ways during polymerization, by formation of head-to-tail (normal linking) or head-to-head linkages. By comparing infrared and Raman spectroscopic data, it was concluded that the polymers formed are indeed alternating in nature (66). It was additionally concluded that only head-to-tail linkages were observed. The proposed chemical structure is shown below. 

Fourier transform mid-infrared (FTIR), near-infrared (FTNIR), and Raman (FT-Raman) spectroscopy were used for discrimination among 10 different edible oils and fats, and for comparing the performance of these spectroscopic methods in edible oil/fat studies. The FTIR apparatus was equipped with a deuterated triglycine sulfate (DTGS) detector, while the same spectrometer was also used for FT-NIR and FT-Raman measurements with additional accessories and detectors. The spectral features of edible oils and fats were studied and the unsaturation bond (C=C) in IR and Raman spectra was identified and used for the discriminant analysis. Linear discriminant analysis (LDA) and canonical variate analysis (CVA) were used for the disaimination and classification of different edible oils and fats based on spectral data. FTIR spectroscopy measurements in conjunction with CVA yielded about 98% classification accuracy of oils and fats followed by FT-Raman (94%) and FTNIR (93%) methods however, the number of factors was much higher for the FT-Raman and FT-NIR methods. 

Raman and infrared spectra have also been compared for a series of 1,4-benzodiazepines, including diazepam (Vallium) and of closely related compounds [16,17]. The complementary nature of these two vibrational spectroscopic techniques was highlighted and the data provided spectral features that allowed identification of the drugs. The value of Fourier transform Raman spectroscopy using a near-infrared excitation source was also demonstrated for these heterocyclic molecules which have a tendency to fluoresce with visible radiation from conventional dispersive Raman spectrometers. 

Finally, it is evident that SERS should be considered from a wider perspective and comparing the performance of SERS with other techniques can always be useful. For example, fluorescence microscopy and spectroscopy are extremely sensitive and widely used techniques in many areas of the life sciences. Further development and expanding of other surface-enhanced spectroscopic techniques such as surface-enhanced infrared absorption (SEIRA), surface-enhanced fluorescence (SEF) and tip-enhanced Raman scattering (TERS) are also highly desirable. It is highly appreciable so that these techniques will help to refine information obtained by SERS in many bioanalytical, biomolecular and medical studies. 

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