Solid-state Vibrational Spectroscopies

Vibrational spectroscopies (mid-IR, near-IR, Raman) play an important role in polymer/additive analysis. Optical advances as well as spectacular advances in computing technology and data processing algorithms have greatly impacted vibrational spectroscopy over the past 25 years (cfr Table 1.5). Rapid digital data acquisition is required for FTIR, FT-Raman or CCD-Raman spectroscopy. The raw data obtained from these instruments must always be manipulated before a recognisable spectrum can be displayed. 

Although the three spectroscopic techniques are very different in several aspects, their basic physical origin is the same absorption in mid-IR and NIR, and scattering in Raman, as a consequence of molecular vibrations. Due to the different excitation conditions, the relationships between the observed spectral intensities and the chemical nature of the vibrating molecules vary significantly. 

Where scanning mid-IR and NIR spectroscopy operate with a polychromatic source from which the sample absorbs specific frequencies corresponding to molecular vibrational transitions, in Raman spectroscopy the sample is irradiated with monochromatic laser light whose frequency may vary from the 

VIS to the NIR region. Multicomponent analysis can be achieved for samples containing up to ten components through a variety of multivariate statistical algorithms. Table 1.6 compares the main characteristics of vibrational spectroscopies. As far as the quantitative evaluation of vibrational spectra is concerned, mid-IR and NIRS follow Beer s law whereas the Raman intensity is directly proportional to the concentration of the compound to be determined. 

Near-infrared reflectance measurements are non-desfructive, require no direct contact with the sample analysed (often an important factor in maintaining hygienic processing conditions), and can provide real-time analytical information. They have become possible by combining two fairly recent 

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The development of methods and instrumentation, especially in the high field range, will already open up quite new areas of uses already in the near future. These may at least partly replace and complete solid-state vibration spectroscopy in the polymer field in cases where the amount of material is not the limiting factor. As far as we are able to predict the future, the development of exact quantitative methods of analysis, in particular, will rapidly develop to a high degree of accuracy. 

The theory is carefully presented with emphasis on how theory and experiment connect in the interpretation of INS data and in the computational modelling of INS spectra. A particular emphasis is on solid state vibrational spectroscopy and the exploitation of ab initio computational methods and modem computational techniques generally. 

Infrared, and more recently Raman spectroscopy, have been widely used for the qualitative and quantitative characterization of polymorphic compounds of pharmaceutical interest (for the sake of brevity, the term polymorphism will encompass polymorphs, pseudo-polymorphs, hydrates, and solvates). Since solid-state vibrational spectroscopy can be used to probe the nature of polymorphism on the molecular level, these methods are particularly useful in instances where full crystallographic characterization of polymorphism was not found to be possible. 

Both solution and solid-state vibrational spectroscopy have been employed to characterize the reaction shown above. In addition. X-ray powder diffraction of the recovered solids from the uranium experiment shows the presence of both (HjO" ") (SbFg) and UF4 -2SbF5. Raman spectroscopy of the solid mixture after vacuum removal of the solvent features bands at 667,561, and 295 cm due to the Vj, V2, and Vj stretching and bending modes of SbF g, respectively. The infrared spectrum of the solid also shows a broad band at 3058 cm (vj) and a sharp band at 1623 cm" (V4) due to the (HjO ) moiety. Little difference between the spectra reported for pure (HjO" ") (SbFg) (Christe et al. 1984) and our heterogeneous mixtures was observed. Therefore,... 

Solid-state vibrational spectroscopy/microscopy (Amigo 2010 Breitkreitz and Poppi 2012 Chen et al. 2011 Gendlin et al. 2008 J0igensen et al. 2(X)9 Kazarian and Ewing 2013 McIntosh et al. 2012 Pavia et aL 2001 Prats-Montalban et al. 2012 Reich 2005 Van Eerdenbrugh and Taylor 2011 Zeitleretal. 2(X)7)... 

For example, in a recent tutorial, Kettle and co-authors described the solid-state vibrational spectroscopy of bis(dicarbonyl-77-cyclopentadienyliron) [4]. Although it is well established, solid-state spectroscopy is given cursory treatment in standard physical chemistry textbooks. The iron compound makes an interesting case study because its cis and trans isomers crystallize in the same space group. Raman and infrared spectroscopy are given equal consideration in the discussion. 

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