Line broadening static

Liquid crystals confined into cylindrical cavities are the most suitable systems for deirteron NMR studies of the interfacial liquid crystal-substrate interactions. There are, however, other systems of confined liquid crystals, which are more important for applications (PDLC and H-PDLC materials), or have been the object of intensive theoretical studies. The latter are composite systems with a random network of pores like liquid crystals in nano-pore glasses, aerogels and aerosils. Unfortunately, in all these cases NMR spectroscopy alone cannot yield accurate information on the surface-or constraint-induced order in the high-temperature phase as no quadrupole splitting is observed. The nature of the spectral line-broadening (static or dynamic) has to be established using NMR relaxometry. Current NMR results related to these systems will be briefly discussed in Sect. 2.4. 

Stress in crystalline solids produces small shifts, typically a few wavenumbers, in the Raman lines that sometimes are accompanied by a small amount of line broadening. Measurement of a series of Raman spectra in high-pressure equipment under static or uniaxial pressure allows the line shifts to be calibrated in terms of stress level. This information can be used to characterize built-in stress in thin films, along grain boundaries, and in thermally stressed materials. Microfocus spectra can be obtained from crack tips in ceramic material and by a careful spatial mapping along and across the crack estimates can be obtained of the stress fields around the crack. ... 

Line broadening due to inhomogeneity in the static magnetic field. Ho, as well as in the rf pulse Hj, can contribute to the observed resonance. However, studies of standard sairples, of known natural linewidths, enable the contributions from this source to be determined. In the present case these causes contribute only a few percent, i.e., a few Hz, to the total linewidth and are thus inconsequential to the present problem. Before discussing the different motional contributions to the linewidth. 

The observed fivefold symmetry in the 1H and 13C NMR spectra even at very low temperature (— 150°C) with no line broadening leaves only two alternatives for the structure of the dication the nonclassical fivefold symmetrical, static structure 437 or... 

As introduced in Section 3.1, Forster theory assumes that there is no inhomogeneous line broadening, i.e. static disorder, in the spectra of donor emission and acceptor absorption. However, if one considers an ensemble of inhomoge-neously broadened spectra, the spectral overlap is given by ... 

Figure 14.1 ID spectra of a typical rubber, styrene-butadiene-rubber (SBR). a) Static spectrum acquired at a Larmor frequency of 500 MHz. The dipolar coupling is motionally averaged and different lines can be distinguished although they are still broadened by the residual dipolar couplings, b) MAS spectrum of the same sample at a MAS spinning frequency of 15 kHz. The line-broadening due to anisotropic spin interactions, e.g., residual dipolar couplings, is removed...

Figure 1 Simulated MAS (rows Ml and M2) and QCPMG (rows Q1 and Q2) spectra corresponding to the static limit (fc=10-9 Hz) of a two-site jump process corresponding to parameter sets P1-P5 in Table 1. In rows Q1 and Ml, the Hamiltonian includes the only HQ(1) whereas both HQ(1) and Hq(2) are included for the spectra in rows Q2 and M2. Gaussian line broadenings of 30 (A), 50 (B) or 75 (C-E) Hz were applied prior to Fourier transformation.

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