Solid high-resolution spectra

Our aims in this chapter are, first, to describe the important interactions in sufficient detail to explain the principal features in the NMR spectra of solids and, second, to discuss methods that have been developed to overcome selectively the effect of some of these interactions and thus to produce in solids high resolution spectra that are reminiscent of those found in liquids, albeit with line widths... 

Owing to the differences in both the nature and magnitude of the homo-and hetero-nuclear dipolar interactions, the process of eliminating the dipolar interactions to obtain a high resolution spectrum in the solid state is slightly different for protons and carbons, respectively, and will be reviewed separately in following... 

Fig. 1. Internal reflection spectra for HF-treated Si(lll) surfaces, (a) Surface treated with buffered HF, pH 9-10 (solid curve), dilute HF (H2O/HF 100 1) (broken curve) (b) s-polarization spectrum for surface treated with buffered HF, pH 9-10. Inset high-resolution spectrum for Si(lll) treated with buffered HF, pH 9-10 [20].

To obtain high-resolution spectrum for solid matter, we have to eliminate the effect of Ho and furthermore average that of Hs, because Hs is a tensor of rank 2. In the solid-state NMR, the high-resolution spectrum is obtained by com-... 

Figure 3. Statistical analysis of the intensity distribution of the high-resolution spectrum of C2 H2 at about 26,500 cm 1, including nearly 4000 lines. (Adapted from Ref. 55.) The solid line is the maximum entropy distribution (cf. Ref. 56) given by Eq. (3) with v = 3.2.

If the dipolar couplings are not too large, or if they were partially averaged by molecular motion, fast MAS (—35 kHz) used by itself can be employed to obtain a high-resolution spectrum. In such cases, many of the complex experiments designed for liquids ean be applied to these "soft" solids. ... 

In a nuclear magnetic resonance measurement in solution, the direct dipolar interaction Xo actually disappears because, due to rapid molecular motion, the interspin (internuclear) vectors are rapidly space-averaged within the time-scale of a measurement. Hence, the terms Xs and Xj are detectable as sharp lines or splittings in a high-resolution spectrum of H or and they can be related to detailed molecular structure or conformation of the substance investigated. In a solid, on the contrary, the directions of the internuclear vectors are stationary even if they are distributed randomly in space. Then, X gives a very wide linewidth to the zeroth-order absorption line and completely masks all lines due to Xs and Xj. 

As mentioned in Sec. LA, interactions other than isotropic chemical shifts and scalar couplings dominate the NMR of solids. If a high-resolution spectrum is desired, these other effects must be deliberately removed molecular motion alone will not average them during the course of the measurement. Alternatively, experiments have been designed which isolate these interactions—dipolar coupling, quadrupolar coupling (in appropriate nuclei), and chemical-shift anisotropy—and exploit their useful features to provide information about the system under study. 

NMR can be used to study the relaxation of polymer molecules in the soUd state. Slower motion will render broader and overlapped spectra, as is generally seen in solid samples. As molecular motion becomes faster, as in solutions or in polymers much above the glass transition temperature, the screening constant will be averaged and the spectrum will become narrower, yielding a high resolution spectrum. The spectral Hne shape can therefore provide information on molecular motions in the samples. 

Figure 10.5 Comparison of spectrum (convoluted with Gaussian specified by standard deviation ) of monodimensional harmonic model computed according to fully quantum methods (high-resolution spectrum, c = 100 cm , black dotted fine low-resolution spectrum, cr = 300cm , green solid line) and classical approximation described in Section 10.4.3. (low-resolution spectra, computed according to Eq. 10.83, red dashed line, or neglecting R function, blue dot-dashed line), (a) Allowed (Franck-Condon) transition at 300 K in presence of significant displacement 5 of equihbrium positions and moderate change in harmonic...

The and C NMR spectra of a polymer can be obtained either in the solid state or in solution. If the polymer before and/or after photodegradation is soluble, a high-resolution spectrum can be obtained (Figs 10.80,10.81). 

It is important to point out that all the authors have overlooked the node and have taken 2 qualitatively as the C=C ring stretching mode and have drawn qualitative chemical conlusions. On the other hand Harada [123] has clearly and very bravely identified in the very complex high resolution spectrum of solid Thg the mode as the... 

ICP-OES is one of the most successful multielement analysis techniques for materials characterization. While precision and interference effects are generally best when solutions are analyzed, a number of techniques allow the direct analysis of solids. The strengths of ICP-OES include speed, relatively small interference effects, low detection limits, and applicability to a wide variety of materials. Improvements are expected in sample-introduction techniques, spectrometers that detect simultaneously the entire ultraviolet—visible spectrum with high resolution, and in the development of intelligent instruments to further improve analysis reliability. ICPMS vigorously competes with ICP-OES, particularly when low detection limits are required. 

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