NMR line-narrowing

Sonicated particles can also have their motion influenced by the presence of cavities remote from their surfaces. This may arise through the action of shock waves propagated from the collapse of unstable cavities. Since these shock waves have been suggested to be capable of causing metal particles to fuse, it is not surprising that they are capable of increasing the number of interparticle collisions. In turn, these, like microjets, can result in the oscillation of the particles about their Dysthe equilibrium positions with such rapidity that NMR line-narrowing can be achieved. 

For at least two polymers, polytetrafluoroethylene 25, 62) and poly- trans-l,4-butadiene) 4, 25), relaxation processes accompanying crystal-crystal phase transitions are found. Sharp NMR line narrowing has been observed at the transition temperature for various normal paraffins 44)-... 

DQ) MAS spectroscopy. The authors give an example of the state of the art in solid state H NMR line narrowing experiments using combined rotation and multiple pulse decoupling (CRAMPS), and indicate that the newest variants of this experiment have yielded line widths as low as 60 Hz for the aliphatic protons resonances of the amino acid L-alanine. 

The prefactor /, has also been associated with the Debye frequency of the lattice modes. The diffusion of H in the fee metals Pd, Ni, Cu and Al, reduced to the elementary hop rate between the neighbouring sites, shows classical behaviour (6.2) above room temperature . Note that many experimental methods, including neutron inelastic and quasielastic scattering, NMR line narrowing and spin-lattice relaxation, internal friction and ultrasonic damping, can give important information about the H motion on various timescales, that complements that obtained from ordinary diffusion measurements. 

Chmelka, B.R, Zwanziger, J.R Solid-State NMR Line Narrowing Methods for Quadrupolar Nuclei Double Rotation and Dynamic-Angle Spinning. Vol. 33, pp. 79-124 Clayden, N.J. Solid State NMR of Synthetic Polymers. Vol. 29, pp. 91-126 Cohen, J.S., see Kaplan, O. 

P.B. Smith Temperature affects dynamics, dynamics affect NMR linewidths, and dynamics also affect flow. These effects are observed not only in linear polymers but in crosslinked polymers as well, highly crosslinked polymers, too, I might add, where I just don t see how you can have flow. I think flow is a function of the molecular dynamics, as are the NMR linewidths. The molecular dynamics give rise to both parameters rather than flow causing NMR line narrowing. 

There is a second relaxation process, called spin-spin (or transverse) relaxation, at a rate controlled by the spin-spin relaxation time T2. It governs the evolution of the xy magnetisation toward its equilibrium value, which is zero. In the fluid state with fast motion and extreme narrowing 7) and T2 are equal in the solid state with slow motion and full line broadening T2 becomes much shorter than 7). The so-called 180° pulse which inverts the spin population present immediately prior to the pulse is important for the accurate determination of T and the true T2 value. The spin-spin relaxation time calculated from the experimental line widths is called T2 the ideal NMR line shape is Lorentzian and its FWHH is controlled by T2. Unlike chemical shifts and spin-spin coupling constants, relaxation times are not directly related to molecular structure, but depend on molecular mobility. 

For rigid Si-F bonds, the 19F CSA is characterized by a span, Q = Sn - S33, of about 80 ppm [150]. This parameter describes the total static linewidth of 19F NMR of rigid Si-F bonds in zeolites. Line narrowing (reduced span values) is observed, when the fluoride ion carries out motional jumps between two or more Si sites. 

Ci-C6 alkanes/interactions among guest molecules H MAS NMR linewidths (effect of molecular motion on MAS line narrowing) [198]... 

In a sample of bulk Pt metal, all of the nuclei have the same interaction with the conduction electrons and thus see the same local field. The resulting NMR line is quite narrow. However, in our samples of small Pt particles, many of the nuclei are near a surface where the state of the conduction electron is disturbed. This tends to reduce the Knight shift for these nuclei. Since the Pt particles in our samples are of many different sizes and shapes, this reduction in the Knight shift is not the same for every nuclear spin near a surface. Thus, we obtain a broad "smear" of Knight shifts resulting in the lineshapes of Figure 5. 

In general, liquid-state NMR is preferable as a starting point over SSNMR for several compelling reasons. The primary reason is due to the ability of liquid-state NMR to yield much narrower lines. In practice, liquid-state NMR line shapes are typically an order of the magnitude or more narrower than the solid state. This provides much greater spectral resolution and often an apparently greater signal-to-noise ratio for liquids spectra as compared with solids spectra. NMR... 

An interesting application of the motional narrowing concept arises in the double NMR technique BS). In this technique the contribution to the NMR line width of nuclei (A) in a solid by the dipolar fields of dissimilar nuclei (B) may be removed by application of a sufficiently strong rf field at the resonance frequency of the B nuclei. With Hib A/Ib, A/Ia where AH is the line width, flipping of B nuclei by the Hib field will cause fluctuations in the dipolar fields of B nuclei at the A nuclei which are rapid compared to T2a and hence cause narrowing of the NMR line of the A nuclei. This effect has been observed in several different solids of the AB type 5S,6A). 

A large research group at Indiana University (18, 80, 105, 120) has obtained splendid line-narrowed B NMR spectra which, however, should also favor I-A15. Yet if a continuum of BE hydrogens (especially in the aracAno-boranes) is simply accepted, then polemics as to whether the bridge hydrogen or endohydrogen structures are correct are of little substance. 

Supercritical fluids possess several advantages from the NMR point of view [249]. The very low viscosity of these solvents produces a beneficial line-narrowing effect on quadrupolar nuclei such as Co, Cr, Zr, Mo, Mn and due to... 

Low frequency spectra of liquids are notably deficient of any structure, and it has long been hoped that a technique would be discovered that provides the same type of line narrowing enjoyed in echo-based electronic and NMR spectroscopy. Tanimura and Mukamel observed that such a technique was possible, and proposed a two-time interval, fifth-order Raman pulse sequence capable of distinguishing, for example, inhomogeneous and homogeneous contributions to the lineshape.[4] The pulse sequence, shown in Fig. 1, is simply an extension of conventional time-domain third-order Raman-based methods. At the... 

The liquid sample is placed in a narrow glass tube. One of the problems in NMR is broadening of the lines due to small inhomogeneities in B0. Spinning the sample tube rapidly causes the nuclei to see an averaged field and narrows the NMR lines (see Section 8.9). 

Hence <3cos20- 1> = 0, and the direct dipole-dipole coupling between two magnetic nuclei vanishes for liquids and gases. Thus the NMR lines of liquids and gases are narrow, allowing chemical shifts to be observed we have high-resolution NMR. 

Although crosslinked polymers and polymer gels are not soluble, the spectra of swollen, low crosslink density networks exhibit reasonably narrow C-13 NMR line widths, sufficiently resolved to reveal details of microstructure 13S). Thus, recording the spectra under scalar low power decoupling yields characterization information and some dynamic measurements, concerning T, T2 (line widths) and nuclear Overhauser enhancement (NOE) for lightly crosslinked polymers. 

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