Nuclear magnetic resonance correlation time

The nuclear magnetic resonance relaxation times for the protons of water adsorbed to saturation in a high-purity specimen of zeolite 13-X have been measured between 200° and 500°K. The data can be accounted for by the model of an intracrystalline fluid which is about 30 times as viscous as bulk water at room temperature, shows a broad distribution of molecular mobilities, and is about as dense as liquid water. The median correlation time (time between molecular flights) is... 

Woessner D E 1996 Brownian motion and correlation times Encyclopedia of Nuclear Magnetic Resonance ed D M Grant and R K Harris (Chichester Wiley) pp 1068-84... 

Liquids are difficult to model because, on the one hand, many-body interactions are complicated on the other hand, liquids lack the symmetry of crystals which makes many-body systems tractable [364, 376, 94]. No rigorous solutions currently exist for the many-body problem of the liquid state. Yet the molecular properties of liquids are important for example, most chemistry involves solutions of one kind or another. Significant advances have recently been made through the use of spectroscopy (i.e., infrared, Raman, neutron scattering, nuclear magnetic resonance, dielectric relaxation, etc.) and associated time correlation functions of molecular properties. 

PAD (perturbed angular distribution) is a variation of PAC with nuclear excitation by a particle beam from an accelerator. QMS is quasielastic MdBbauer-spectroscopy, QNS is quasielastic neutron spectroscopy. For MOBbauer spectroscopy (MS), perturbed angular correlation (PAC), and /J-nuclear magnetic resonance (/3-NMR), the accessible SE jump frequencies are determined by the life time (rN) of the nuclear states involved in the spectroscopic process. Since NMR is a resonance method, the resonance frequency of the experiment sets the time window. With neutron scattering, the time window is determined by the possible energy resolution of the spectrometer as explained later. 

For the investigation of the molecular dynamics in polymers, deuteron solid-state nuclear magnetic resonance (2D-NMR) spectroscopy has been shown to be a powerful method [1]. In the field of viscoelastic polymers, segmental dynamics of poly(urethanes) has been studied intensively by 2D-NMR [78, 79]. In addition to ID NMR spectroscopy, 2D NMR exchange spectroscopy was used to extend the time scale of molecular dynamics up to the order of milliseconds or even seconds. In combination with line-shape simulation, this technique allows one to obtain correlation times and correlation-time distributions of the molecular mobility as well as detailed information about the geometry of the motional process [1]. 

Rotational diffusion is characterized by the mean square angular deviation during the time interval At (0 ) = GDrAi. Highly anisotropic motion, which is typical for lipid molecules in the membrane, is usually described by two rotational diffusion coefficients Dr and Dri, which correspond to diffusion about the long diffusion axis and perpendicular to it, respectively. The diffusion coefficients are related to corresponding rotational correlation times measured by nuclear magnetic resonance (NMR), electron spin resonance (ESR), fluorescent depolarization, and so on, as ... 

The potential of nuclear magnetic resonance spectroscopy for studying liquid crystalline systems is discussed. Typical spectra of nematic, smectic, and cholesteric mesophases were obtained under high resolution conditions. The observed line shape in the cholesteric phase agrees with that proposed on the basis of the preferred orientation of this phase in the magnetic field. The line shapes observed in lyotropic smectic phases appear to be the result of a distribution of correlation times in the hydrocarbon portions of the surfactant molecules. Thermotropic and lyotropic phase transitions are easily detected by NMR and agree well with those reported by other methods. The NMR parameters of the neat and middle lyotropic phases allow these phases to be distinguished and are consistent ivith their proposed structures. 

This report presents a determination of the fluidity of water adsorbed to saturation in zeolite 13-X. As a measure of the fluidity, the time between molecular jumps or correlation time, r, is employed it has been derived from measurements of nuclear magnetic resonance (NMR) relaxation times via the theory of Bloembergen, Purcell, and Pound (BPP)... 

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