Spin-lattice relaxation linear

NMRD studies (0.01-30 MHz) on bentonite suspensions showed that the water-proton spin-lattice relaxation rates are dominated by magnetic interactions with paramagnetic centers entrapped in the mineral matrix (89). The 1/Ti values were linearly dependent on the concentration of the... 

An interesting application in porous silica glass employs deuterium spin-lattice relaxation rates in selectively deuterated pyridine (50). The pore-size dependence shown in Fig. 20 is linear in the reciprocal of the pore radius for both the para and ortho positions, but the significant difference in the relaxation at these two positions precludes analysis by an isotropic... 

Spin-lattice relaxation times were measured by the fast inversion-recovery method (24) with subsequent data analysis by a non-linear three parameter least squares fitting routine. (25) Nuclear Overhauser enhancement factors were measured using a gated decoupling technique with the period between the end of the data acquisition and the next 90° pulse equal to eibout four times the value. Most of the data used a delay of eibout ten times the Ti value. (26)... 

Figure 8. Plot of spin-lattice relaxation time against temperature, at 67.9 MHz, for linear and branched PE. Linear PE from Ref. 17, (%) linear PE this work, ( O ) branched PE this work, ( j.

A similar continuity in the Tj s through the melting temperature was previously reported for linear polyethylene. (17) We have now investigated the temperature dependence of this quantity, for this polymer, in more detail and have also studied a low density (branched) polyethylene. The results for the poly-ethylenes are summarized in Fig. 8. The new data reported here substantiate the conclusion previously reached for linear polyethylene. A similar conclusion can now be reached for the baclc-bone carbons of low density (branched) polyethylene. The melting temperature for this particular sample, under the crystallization conditions studied, is less than 110°C. (33) Thus, the spin-lattice relaxation parameters for the bac)cbone carbons are the same for both the linear and branched polymers over the temperature range studied here. Changes that occur in Tq as the temperature is reduced below 0°C involve other considerations and will be discussed in detail elsewhere. (22)... 

Proton NMR relaxation parameters have also been determined for polyethylene ( ) and polyethylene oxide (39) in the melting region. The apparent contradiction between the proton spin-lattice relaxation parameter for a high molecular weight linear polyethylene sample at its melting point, with the relaxation measurements, has previously been pointed out. (17) This discrepancy is still maintained with the more detailed results reported here for both types of polyethylene. For the proton relaxation a small, but distinct, discontinuity is reported at the melting teirperature. (38)... 

Most relaxation measurements are conducted in such a way as to record the resulting magnetization after a variable delay, r, during which the initially created state is allowed to relax. In the spin-lattice relaxation experiment, the T relaxation time can be evaluated by non-linear three-parameter fitting of the following expression [31] to the intensities ... 

The precipitates of PVPh/PDMA from methanol and acetone solutions were examined by CPMAS NMR [51], and evidence for specific interaction was obtained with a 3 ppm shift in the phenolic carbon resonance peak. The proton spin-lattice relaxation times Tj were shorter than those predicted by a linear model, though the rotating frame spin-lattice relaxation times Tjp of the com-... 

Fatkullin NF, Kimmich R, Kroutieva M (2000) The twice-renormalised Rouse formalism of polymer dynamics Segment diffusion, terminal relaxation, and nuclear spin-lattice relaxation. J Exp Theor Phys 91(1) 150-166 Ferry JD (1980) Viscoelastic properties of polymers, 3rd edn. Wiley, London Ferry JD (1990) Some reflections on the early development of polymer dynamics Viscoelasticity, dielectric dispersion, and self-diffusion. Macromolecules 24 5237-5245 Ferry JD, Landel RF, Williams ML (1955) Extensions of the Rouse theory of viscoelastic properties to undilute linear polymers. J Appl Phys 26 359-362 Fikhman VD, Radushkevich BV, Vinogradov GV (1970) Reological properties of polymers under extension at constant deformation rate and at constant extension rate. In Vinogradov GV (ed) Uspekhi reologii polimerov (Advances in polymer rheology, in Russian). Khimija, Moscow, pp 9-23... 

The determiiiation of spin-lattice relaxation time (Tj) and correlation time (r) using NMR spectroscopy (66) provides direct information about the intramcdec-ular motion of cydic peptides. Recently, Fossel et al. (67) determined r values with Cyclo-(Gly2), Qydo-(Gly-Pro), Cyclo-(Pr02), and Cydo- Pro-D-Pro) in D2O solution, and the r values were compared with those for the correspmiding linear dipeptides. 

Redfield limit, and the values for the CH2 protons of his- N,N-diethyldithiocarbamato)iron(iii) iodide, Fe(dtc)2l, a compound for which Te r- When z, rotational reorientation dominates the nuclear relaxation and the Redfield theory can account for the experimental results. When Te Ti values do not increase with Bq as current theory predicts, and non-Redfield relaxation theory (33) has to be employed. By assuming that the spacings of the electron-nuclear spin energy levels are not dominated by Bq but depend on the value of the zero-field splitting parameter, the frequency dependence of the Tj values can be explained. Doddrell et al. (35) have examined the variable temperature and variable field nuclear spin-lattice relaxation times for the protons in Cu(acac)2 and Ru(acac)3. These complexes were chosen since, in the former complex, rotational reorientation appears to be the dominant time-dependent process (36) whereas in the latter complex other time-dependent effects, possibly dynamic Jahn-Teller effects, may be operative. Again current theory will account for the observed Ty values when rotational reorientation dominates the electron and nuclear spin relaxation processes but is inadequate in other situations. More recent studies (37) on the temperature dependence of Ty values of protons of metal acetylacetonate complexes have led to somewhat different conclusions. If rotational reorientation dominates the nuclear and/or electron spin relaxation processes, then a plot of ln( Ty ) against T should be linear with slope Er/R, where r is the activation energy for rotational reorientation. This was found to be the case for Cu, Cr, and Fe complexes with Er 9-2kJ mol" However, for V, Mn, and... 

Low-spin Fe(iii) porphyrins have been the subject of a number of studies. (638-650) The favourably short electronic spin-lattice relaxation time and appreciable anisotropic magnetic properties of low-spin Fe(iii) make it highly suited for NMR studies. Horrocks and Greenberg (638) have shown that both contact and dipolar shifts vary linearly with inverse temperature and have assessed the importance of second-order Zeeman (SOZ) effects and thermal population of excited states when evaluating the dipolar shifts in such systems. Estimation of dipolar shifts directly from g-tensor anisotropy without allowing for SOZ effects can lead to errors of up to 30% in either direction. Appreciable population of the excited orbital state(s) produces temperature dependent hyperfine splitting parameters. Such an explanation has been used to explain deviations between the measured and calculated shifts in bis-(l-methylimidazole) (641) and pyridine complexes (642) of ferriporphyrins. In the former complexes the contact shifts are considered to involve directly delocalized 7r-spin density... 

FIG. I. Spin-lattice relaxation time of Li in 3-9 M LiClin HiOasafunctionofinverse absolute temperature. Circles experimental relaxation time. 7 ," crosses dipolar contribution, obtained from T,"" and the nuclear Overhauser enhancement factor t). The linear least-squaresfit for the latter yields an activation energy of 3-6kcalmol (16)... 

With a chromatographic technique capable of routinely yielding preparative fractions, quantitative and C FT NMR was the major spectroscopic tool used for chemical characterization. The established utility of and C NMR for characterization of coal products is documented well. Unfortunately, high-resolution C FT NMR is not quantitative normally under operating conditions used typically. (It should be noted that quantitative FT NMR measurements also are not obtained routinely. The problem of variable spin lattice relaxation times (Ti s) is present also in FT NMR. In addition, the greater signal intensity of NMR in comparison with C FT NMR poses an additional potential problem of detector linearity in the FT NMR receiver.) For C FT NMR, variable spin lattice relaxation times (Ti s) and nuclear Over-hauser effects (a result of pseudo random noise decoupling) usually... 

Nuclear spin-lattice relaxation conducting regime. As for the spin sector in the conducting regime, an approach to the 1-D exponent can be attempted looking at the spin-lattice relaxation rate for which the 2k° contribution should become predominant at low temperature where 0deviation from linearity below 150 K or so (Fig. 11), signaling the onset of 2k fluctuations. These AF fluctuations become even more visible when T, is plotted... 

For the same "family" of porous MCM-41 materials, a simple linear relationship between spin-lattice relaxation rate (l/Tj) and the inverse pore radius (1/tp) was found by the SINTEF Oslo group (78) ... 

In this section we try to look at the relaxation in a linear triatomic molecule OCS as a neat liquid at variable temperature and magnetic field. We will give an elaborate example of how to separate different relaxation mechanisms from each other. We recall that the spin-lattice relaxation rate 1/Ti of a spin / = nucleus is given as a sum of several possible contributions ... 

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