Resonance line broadening

Dillehay, D.R. (1983) Resonance line Broadening of Alkali Metals in Pyrotechnic Flames, Ph.D. Thesis, Clayton University, St. Louis, Missouri, April 1983. 

In the case of the single phase alloy Smo.5Ybo.5Cu2Ge2 the NMR signal due to copper was not detected and the resonance line broadening beyond the point of detection due to spatial fluctuation of EFG at the copper nuclei explains the reason why rare earths in EuCu2Si2 and YbCu2Si2 appear identical to the copper nuclei. 

Resonance line broadening due to chemical exchange and quadrupole-induced relaxation in the H and nB n.m.r. spectra of some boron-nitrogen adducts ArNMe2,BY3 (Y = halogen) has been observed and used to determine the mechanism of amine scrambling in these adducts.165 This is thought to occur via a unimolecular ionization rather than a B—N bond-rupture process. 

Obviously, the magic angle spinning techniques described briefly above rely on coherent averaging out of resonance line-broadening interactions. An alternative approach is to cause solids to assume the incoherent motion of molecules in the liquid phase. Essentially, two such methods exist. The first is the so-called ultra-fine particle NMR (UFPNMR) method which was proposed originally by Yesinowski [21 ] and developed further by Kimura [22,23]. The second is the sonically induced narrowing of the NMR spectra of solids (SINNMR) that was demonstrated recently by Homer et al. [24,25]. 

Variable power measurements elucidate the saturation behavior of the nuclei. At low powers the NMR signal amplitude increases, and the line width remains unchanged with increasing rf power. At high powers saturation occurs, the resonant line broadens, and finally it decreases in amplitude with increasing rf power. Relaxation times may be eom-puted from saturation data (12). 

Therefore the radiospectroscopy can be considered as a sensitive tool for the size effects investigation in nanomaterials. The theoretical base for above methods application is the description of radiospectroscopy spectra peculiarities due to above size effects with respect to the characteristic features of a nanomaterial. In particular, the disappearance of spontaneous polarization at critical size in ferroelectric nanomaterial should lead to the variation of the spectrum symmetry, while the distribution of the nanoparticle sizes have to result in the inhomogeneous resonance lines broadening. 

Rates of rapid ligand exchange reactions by nuclear magnetic resonance line broadening studies. /. Am. Chem. Soc.,... 

Deviations from harmonic behaviour are also found above about 200 K, however, only for the amorphous samples. These high temperature anharmonicities occur often far below Tg, which is typically around 300-350 K. They are supposed to be caused by residual solvents in the polymer matrix. We have also studied / T) for some polymers with a relatively low Tg of 250-300 K. In f T) decreases rapidly following a V c - T dependence as predicted by mode coupling theory (MCT). This is interpreted as the onset of local processes. Tc represents the transition from non-ergodic to ergodic behaviour, which occurs typically 30-150 K above the macroscopic glass transition temperature Tg. In Fig. 15.10 we show f T) for PROPS. The MCT fit is indicated by the broken line yielding Tc = 306 12 K whereas Tg k, 240 K. Simultaneously with the onset of anharmonic behaviour of/the Mofl-bauer resonance lines broaden and quasi-elastic lines appear close to Tc. 

To observe ENDOR, the concentration of paramagnetic ions should be less than otherwise the resonance lines broaden... 

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