Showing papers on "Relaxation (NMR) published in 1988"
IBM1
TL;DR: Strong, anisotropic magnetic relaxation of the field-cooled and zero-field--cooled magnetization along the principal axes of an Y-Ba-Cu-O single crystal is reported and interpreted with a thermally activated flux-creep model.
Abstract: We report strong, anisotropic magnetic relaxation of the field-cooled and zero-field-cooled magnetization along the principal axes of an Y-Ba-Cu-O single crystal and interpret it with a thermally activated flux-creep model. A simple scaling argument shows that high thermal activation causes magnetic irreversibilities and critical currents to drop below the threshold of detectability at a reduced temperature difference $1\ensuremath{-}t$ proportional to ${H}^{\frac{2}{3}}$, a power frequently observed in experiment and in particular in our crystal.
1,358 citations
Book•
01 Apr 1988
TL;DR: In this article, the chemical shift was used to measure the nuclear overhauser effect in 13C NMR Spectroscopy, and the effect of spin-lattice relaxation was investigated.
Abstract: Foundations of Magnetic Resonance Experimental Techniques of 13C NMR Spectroscopy: Construction of the Spectrometer Fourier Transform Methods Double Resonance Methods in 13C NMR Spectroscopy New Irradiation Procedures Practical Aspects of 13C NMR Measurements The Chemical Shift: Empirical Correlations and Calculations 13C-X-Spin-Spin Couplings 13C Spin-Lattice Relaxation and the Nuclear Overhauser Effect: Fundamentals Measurement of Spin-Lattice Relaxation Times Applications of Spin-Lattice Relaxation Times Dynamic 13C NMR Spectroscopy: Theoretical Basis Applications of Dynamic 13C NMR Spectroscopy Isotope Effects on Equilibria Use of Lanthanide Shift Reagents in 13C NMR Spectroscopy 13C NMR Spectroscopy in the Study of Reaction Mechanisms.
664 citations
TL;DR: In this article, a new resonance effect in solid-state nuclear magnetic resonance (NMR) is described, which involves a combination of magic-angle sample rotation with irradiation of a heteronuclear spin system at the Larmor frequency of one of the spin species.
Abstract: A new resonance effect in solid‐state nuclear magnetic resonance (NMR) is described. The effect involves a combination of magic‐angle sample rotation with irradiation of a heteronuclear spin system at the Larmor frequency of one of the spin species. If the irradiation intensity is such as to establish a match between spin nutation and sample rotation, it is shown that the heteronuclear dipolar spin interaction is selectively reintroduced into the spectrum. This allows small dipolar coupling constants to be measured in the presence of large shielding anisotropies. Applications are anticipated for determination of internuclear distances in materials lacking long‐range order, such as polycrystalline materials, polymers, and surfaces.
373 citations
TL;DR: In this paper, the authors consider two types of structural instability of glassy substances, each of which may be released by a relaxation process with its own characteristic relaxation time, and specific kinetic features.
Abstract: We consider two sorts of structural instability of glassy substances, each of which may be released by a relaxation process with its own characteristic relaxation time, and specific kinetic features. The first of these is the instability against relaxation out of the amorphous state into the crystalline state, while the second is the instability against relaxation within the amorphous state itself. The latter may often involve relaxation out of a homogeneous amorphous phase into a two-phase amorphous structure, but we will not specifically consider this liquid-liquid phase separation process here. In most glasses, the former (which is no more than the characteristic nucleation time) is much longer than the latter time. However, there are important classes of glasses, for instance the metallic glasses, in which the former is in fact the shorter time, a fact which is responsible for the inability to observe the glass transition phenomenon in such substances. In this paper we will be considering the relation between these two times and the specific kinetics of each. The nucleation time has been the subject of theoretical developments over a number of decades, and details will be omitted in order to concentrate on experimental studies of this phenomenon. We will described briefly the recently developed DSC techniques for determining the classical time-temperature-transformation curves for a variety of supercooled liquids, and the relation of these to the nucleation curves. The relaxation process within the amorphous state, which can be observed for cases where the nucleation time is relatively long, has a number of features which currently lack a complete explanation. In most cases the relaxation process is non-Arrhenius in its temperature dependence, nonexponential in its time dependence, and nonlinear in its structural state dependence. Some examples taken from glasses at the “fragile” edge of the deduced viscosity-temperature pattern for glassforming liquids are dealt with in detail, and the distinction between shear stress relaxation and thermodynamic stress relaxation is made. The possibility that near T g the latter relaxation time remains Vogel-Fulcher in form with T 0 ≡ T K (the Kauzmann temperature), in contrast with the common observations for (the decoupled) shear relaxation, is raised. Strong support for this notion is found in the current “specific heat spectroscopy” results of Nagel and co-workers. Microscopic relaxation processes, as observed using spectroscopic probes and neutron scattering techniques, are reviewed, and the difference in non-exponentiality from macroscopic relaxation are examined in the light of current theories. Finally, secondary relaxations in ionic and molecular glasses, and their relation to the fastest of all glassy state relaxation processes, the tunnelling modes (TLS), are briefly considered.
362 citations
TL;DR: A new technique to measure conduction electron relaxation times is described, using nonequilibrium magnetization present in a paramagnetic metal can be detected as an open circuit voltage across an interface between the paramagnet and a ferromagnet.
Abstract: Microscopic models are presented to elucidate the concept of interfacial charge-spin coupling. At the interface between a ferromagnet and a paramagnet, the spin subbands are loosely coupled, an interfacial conductance may be defined for each, and a result of their inequivalence is that an electric current flowing from a ferromagnetic metal into a paramagnetic metal will be partially spin polarized, i.e., will have an associated current of magnetization. The inverse is also true; nonequilibrium magnetization present in a paramagnetic metal can be detected as an open circuit voltage across an interface between the paramagnet and a ferromagnet. Using this effect, a new technique to measure conduction electron relaxation times is described.
282 citations
TL;DR: In this paper, the properties of ten spectral densities relevant for nuclear spin relaxation studies in solids are investigated and a brief review of the appropriate spin-dependent interactions and the various relaxation rates which can be measured is discussed.
233 citations
TL;DR: In this article, the role of solvation dynamics in molecular nonlinear optical line shapes is analyzed using a reduced description based on the time evolution of the density matrix in Liouville space.
Abstract: The role of solvation dynamics in molecular nonlinear optical line shapes is analyzed using a reduced description based on the time evolution of the density matrix in Liouville space. Langevin equations are used to treat the coupling of the solvent to the molecular electronic and nuclear degrees of freedom. Electronic dephasing is calculated using a solvation coordinate which satisfies a generalized Fokker–Planck equation, and vibrational relaxation is related to the solvent viscosity and friction. The combined effect of both processes is incorporated into appropriate multitime correlation functions which are evaluated using a Liouville‐space generating function. The present eigenstate‐free approach is particularly suitable for calculating spectral line shapes as well as rate processes (isomerization, electron transfer) of large polyatomic molecules in condensed phases.
175 citations
TL;DR: The viscosity and temperature-controlled dynamical behavior of rhodamine dyes in the excited state has been investigated by stationary and time-resolved fluorescence measurements using synchrotron radiation.
157 citations
TL;DR: In this article, a 2D NMR technique for measurement of {sub 13}C T{sub 1} values in proteins previously reported has been applied to the determination of spin-lattice relaxation times for the β-carbons of basic pancreatic trypsin inhibitor (BPTI).
Abstract: A heteropolar 2D NMR technique for measurement of {sub 13}C T{sub 1} values in proteins previously reported has been applied to the determination of spin-lattice relaxation times for the {gamma}-carbons of basic pancreatic trypsin inhibitor (BPTI). The technique is described in some detail as applied to BPTI. The lack of dramatic variations noted for T{sub 1} values is taken as assurance that measurements of nuclear Overhauser effects for determination of protein structures in solution are not significantly biased by internal motions, at least as far as the backbone of the protein is concerned. 6 refs., 4 figs.
154 citations
TL;DR: In this paper, the spin diffusion in 13C NMR of double 13C-labeled sodium acetate trihydrate (SAC) and in 31P NMRI of zinc(II) bis(O,O′-diethyldithiophosphate)(ZNP) has been studied under magic-angle spinning conditions.
Abstract: Spectral spin diffusion in 13C NMR of double 13C-labelled sodium acetate trihydrate (SAC), and in 31P NMR of zinc(II) bis(O,O′-diethyldithiophosphate)(ZNP) has been studied under magic-angle spinning conditions. Spin-diffusion time constants, TSD, were determined from the intensities of the spinning sidebands in experiments using rotation-synchronized DANTE pulse sequences, at several different spinning frequencies. The theory of Suter and Ernst, developed for spectral spin diffusion in single crystals, was extended to the case of polycrystalline samples rotating under magic-angle spinning conditions. We considered two mechanisms for the spin diffusion, i.e. dipolar interaction and J-coupling. The spin-diffusion time constants, TSD, were related to the zero-quantum lineshape functions in a manner similar to the theory of Suter and Ernst. The zero-quantum lineshape functions were estimated from the observed single-quantum lineshape functions. In the present studies the dependence of the experimental values for TSD on the rotational frequency vr are in good agreement with those calculated from the theory based on the dipolar interaction mechanism. The values of TSD for SAC showed a deep minimum at Δω≈ 2ωr, and a shallow minimum at Δω≈ 3ωr. This phenomenon is rotational relaxation resonance.
153 citations
TL;DR: In this paper, the authors obtained 17 O nuclear magnetic resonance spectra of a variety of 17 O-labeled solids using high-field static and "magic-angle" sample spinning techniques, together with 1 H cross polarization and dipolar decoupling.
TL;DR: An anomalous temperature dependence of Cu nuclear spin-lattice relaxation time T 1 has been observed for both the Cu1 chain and Cu2 plane sites of YBa 2 Cu 3 O 6.91 (T c =90 K).
Abstract: An anomalous temperature dependence of Cu nuclear spin-lattice relaxation time T 1 has been observed for both the Cu1 chain and Cu2 plane sites of YBa 2 Cu 3 O 6.91 ( T c =90 K) and discussed in connection with spin fluctuations and an anisotropic energy gap which nucleates in the vicinity of Cu2 nuclei.
TL;DR: In this article, it was shown that water molecules reorient with tetrahedral symmetry in polycrystalline hexagonal ice, and that the reorientational rates required to produce similar effects on the patterns are scaled according to the magnitudes of the anisotropic spin interactions.
Abstract: Molecular reorientation in polycrystalline hexagonal ice, ice I/sub h/, has been directly observed by deuterium NMR and deuterium-decoupled proton NMR. The dynamics are seen as exchange broadening of powder patterns. The reorientational rates required to produce similar effects on the patterns are scaled according to the magnitudes of the anisotropic spin interactions, /approximately/ 6 kHz for the proton-shielding anisotropy or /approximately/ 200 kHz for the deuterium quadrupolar coupling in water. Because of the differing sizes of these two interactions, the two methods are complementary for studying reorientation over the temperature range 200-267 K. The results show that water molecules reorient with tetrahedral symmetry in ice. Line-shape simulations using the assumption of tetrahedral reorientation are in accord with the experimental spectra and give rates directly comparable to the temperature-dependent Debye correlation time, /tau//sub D/, from dielectric relaxation. 16 references, 4 figures.
TL;DR: In this article, the influence of inhomogeneous dielectric response on the dynamics of solvation of ions and dipoles is investigated, and the deviation of the average relaxation time from that predicted for a homogeneous continuum solvent is shown.
Abstract: The influence of an inhomogeneous dielectric response on the dynamics of solvation of ions and dipoles is investigated. Solvent models considered include discrete shell models as well as models in which the solvent dielectric constant varies continuously as a function of distance from a spherical solute. The effect of such dielectric inhomogeneity is to introduce additional, slower relaxation times into the solvation response when compared to the homogeneous case. For all models studied, the deviation of the average relaxation time from that predicted for a homogeneous continuum solvent increases as the dielectric constant and the length parameter, which specifies the rapidity of approach to bulk behavior, increase. For a given solvent model the solvation response to a change in a point dipole moment is slower than the response to a charge jump. The continuum results are compared to a recent molecular model based on the mean spherical approximation. The comparison suggests that deviations from homogeneous continuum behavior in the molecular model can be accounted for by inhomogeneity of the solvent dielectric constant extending only over the first solvation shell. Predictions of inhomogeneous continuum models are also compared to experimental data. Both the observed dependence of average relaxation time on dielectric constant, and the detailed time dependence of the relaxation in high dielectric constant solvents can be rationalized on the basis of such models.
TL;DR: A linear relation was found between the inverse of the weight fraction of tissue water and the spin‐lattice relaxation rate, R1, based on a fast proton exchange model for relaxation, which can be used to predict the amount and/or increase in tissue water due to water‐elevating processes such as edema.
Abstract: Proton relaxation times T1 and T2 of macromolecular solutions, bovine brain tissues, and experimental cat brain edema tissues were studied as a function of water concentration, protein concentration, and temperature. A linear relation was found between the inverse of the weight fraction of tissue water and the spin-lattice relaxation rate, R1, based on a fast proton exchange model for relaxation. This correlation was also found for the spin-spin relaxation rate, R2, of gray matter samples and macromolecular solutions at low concentrations. Concentrated solutions of protein-water samples showed an enhanced relaxation due to viscosity effects. The T2 of white matter was considerably lengthened with elevated water concentration, but showed no straightforward relation with the total tissue water content. The relaxation times of all samples increased with temperature, supporting the assumption of fast proton exchange in the model for relaxation. This was not found for white matter, in which T2 decreased with increasing temperature, which indicated that intermediate or even slow exchange was present. The relation found between relaxation times and tissue water content can be used to predict the amount of and/or increase in tissue water due to water-elevating processes such as edema. © 1988 Academic Press, Inc.
TL;DR: In this article, the magnetic field and temperature dependence of the rates for all two-body spin exchange and dipolar transitions among hyperfine levels in cryogenic H gas was calculated by means of the coupled-channels method.
Abstract: We calculate the magnetic field and temperature dependence of the rates for all two-body spin-exchange and dipolar transitions among hyperfine levels in cryogenic H gas by means of the coupled-channels method. A description of this method and its practical application is presented. A simple interpretation of the rates is given, in some cases with associated simple closed-form formulas, based on the degenerate-internal-states approximation.
TL;DR: In this paper, it was shown that the thermal spin-crossover behavior of the complex [Fe(2mephen)3]2+ embedded in various polymer matrices is similar to the solid-state behaviour, and a light-induced long-lived excited state is observed at temperatures below 50 K.
TL;DR: The results of the Brownian dynamics simulation of a hydrocarbon chain in a membrane bilayer described in the preceding paper are used to analyze the 13C NMR T1 relaxation in lipid bilayer vesicles as mentioned in this paper.
Abstract: The results of the Brownian dynamics simulation of a hydrocarbon chain in a membrane bilayer described in the preceding paper are used to analyze the 13C NMR T1 relaxation in lipid bilayer vesicles. The analysis shows that the frequency dependence of the relaxation does not arise from gauche–trans isomerization or from axial rotation of the entire lipid molecule. However, a model in which fast axial rotation (D∥≊2×1010 s−1) and slow noncollective diffusive director fluctuations (D⊥≊1–2×108 s−1) are superimposed on the internal motions quantitatively accounts for both the magnitude and frequency dependence of the T1 data. An effective viscosity for the interior of the bilayer in the range of 1 cp, and a director order parameter of 0.5–0.7 are required to fit the NMR data. Collective effects do not appear necessary for explaining the NMR T1 data in vesicles, although they may be important for multilamellar dispersions.
TL;DR: In this article, an empirical Boltzmann-averaged collision cross section associated with the collision-induced transitions between 129Xe nuclear spin states is obtained as a function of temperature.
Abstract: The nuclear spin relaxation times (T1) of 129Xe in xenon–O2 gas mixtures have been measured as a function of temperature and density at different magnetic fields. This system is used to characterize the intermolecular dipolar relaxation of nuclear spins in the gas phase. An empirical Boltzmann‐averaged collision cross section associated with the collision‐induced transitions between 129Xe nuclear spin states is obtained as a function of temperature.
TL;DR: In this paper, the use of the mean spherical approximation (MSA) in the study of dynamics of polar fluids is further explored in two ways: first, the recent result of Wolynes [J. Chem. Phys. 86, 5133 (1987)] showing that solvation dynamics can be extracted from the static solution of the MSA is further investigated.
Abstract: The use of the mean spherical approximation (MSA) in the study of dynamics of polar fluids is further explored in two ways. First, the recent result of Wolynes [J. Chem. Phys. 86, 5133 (1987)] showing that solvation dynamics can be extracted from the static solution of the MSA is further investigated. The solvation of a dipole in a dipolar fluid is calculated, and compared with an ion in a dipolar fluid. Both cases reduce to simple numerical quadrature. Second, the Smoluchowski–Vlasov equation (SVE) of Calef and Wolynes [J. Chem. Phys. 78, 4145 (1983)] is also reexamined. Using the analytic MSA results, a new set of relaxation times can be defined. In both sections, structural relaxation occurs with multiple relaxation times.
TL;DR: In this paper, it was shown that the Carr-Purcell-Meiboom-Gill (CPMG) sequence is equivalent to a spin-locking sequence in the limit of short interpulse spacing (tcp).
01 Jan 1988
TL;DR: In this article, the theory of electron transfer reactions in polar solvents with two characteristic relaxation times of the polarization of the medium is developed, and it is shown that in some limiting cases the rate of the reaction is limited by the shorter relaxation time of the solvent rather than by the longer one.
Abstract: The theory of electron transfer reactions in polar solvents with two characteristic relaxation times of the polarization of the medium is developed. The theory is beyond the framework of the traditional non-adiabatic approximation of the electron transfer. It is shown that in some limiting cases the rate of the reaction is limited by the shorter relaxation time of the solvent rather than by the longer one. New expressions for the rate constants of the reaction are obtained for these limiting cases.
TL;DR: The nuclear relaxation rate 1/T 1 and the Knight shift have been studied for both the Cu-O plane and chain sites by Cu nuclear quadrupole (NQR) and magnetic resonance (NMR) techniques as mentioned in this paper.
Abstract: The nuclear relaxation rate 1/ T 1 and the Knight shift have been studied for boththe Cu–O plane and chain sites by Cu nuclear quadrupole (NQR) and magnetic resonance (NMR) techniques. Below T c =92 K, 1/ T 1 for the plane site decreases markedly without the enhancement just below T c characteristic for the BCS superconductor, and the Knight shift also shows a more rapid reduction than the BCS prediction, giving evidence of a dominant singlet pairing. In contrast, 1/ T 1 for the chain site shows a weak temperature dependence below T c . This difference of the 1/ T 1 behavior for the plane and chain Cu sites is attributed to the difference of the relaxation processes, i.e., the magnetic and quadrupole relaxation processes, respectively. From both the behaviors of 1/ T and the Knight shift at the plane site, it is pointed out that the Cooper pair may be of a d-type formed by a strong coupling with a large energy gap.
TL;DR: In this article, 23Na and 29Si NMR data on lineshapes, spin-lattice, and spin-spin relaxation times in a series of alkali silicate and aluminosilicate melts from room temperature to about 1200°C are presented.
TL;DR: In this article, a model for non-Arrhenius structural and dielectric relaxation in glass-forming materials is based on defect clustering in supercooled liquids.
Abstract: A model for non-Arrhenius structural and dielectric relaxation in glass-forming materials is based on defect clustering in supercooled liquids. Relaxation in the cold liquid is highly hindered, and assumed to require the presence of a mobile defect to loosen the structure near it. A mild distribution of free-energy barriers impeding defect hopping can generate a wide distribution of waiting times between relaxation events. When the mean waiting time is longer than the time of an experiment, no characteristic time scale exists. This case directly yields the Kohlrausch-Williams-Watts (KWW) relaxation law. A free-energy mismatch between defect and nondefect regions produces a defect-defect attraction, which can lead to aggregation. This may occur in defect-rich “fragile” liquids which also exhibit Vogel kinetics. Defect aggregation and correlation in the “high-temperature” region above the critical consolute temperatureTc is described using the Ornstein-Zernike theory of critical fluctuations. For a defect correlation length divergence (T-Tc)-γ/2, a generalized Vogel law for the structural relaxation time τ results: τ=τ0exp[B./(T-Tc)1.5γ] In the mean-field limit (γ=1) this provides as good an account of dielectric and structural relaxation in glycerol,n-propanol, andi-butyl bromide as does the original Vogel law, and for the mixed salt KNO3−Ca(NO3)2 and B2O2 it also describes kinetics over their entire temperature ranges. A breakdown of the Vogel law in the immediate vicinity ofTg is avoided, and the need to invoke extra low-temperature mechanisms to explain an apparent “return to Arrhenius behavior” is removed.
TL;DR: In this paper, the decay time of a fast liquid crystal modulator employing the transient nematic effect is derived, with potential to achieve ∼50 μs, insensitive to LC thickness, but proportional to (λ/Δn0)2, λ being the wavelength and Δn0 the corresponding birefringence.
Abstract: Transient phase response associated with a small angle relaxation from highly deformed nematic liquid crystal (LC) directors is analyzed experimentally and numerically. Qualitative agreement between computer simulations and experimental results is obtained. Based on these results, decay time of a fast LC modulator employing the transient nematic effect is derived. This decay time is found to be fast (with potential to achieve ∼50 μs), insensitive to LC thickness, but proportional to (λ/Δn0)2, λ being the wavelength and Δn0 the corresponding birefringence.
TL;DR: The loading of a minimum-B-field trap with neutral atomic hydrogen cooled through thermal exchange with liquid-helium surfaces and the limiting decay rate is attributed to dipolar relaxation and found to agree with theory for both magnitude and field dependence.
Abstract: We describe the loading of a minimum-B-field trap with neutral atomic hydrogen cooled through thermal exchange with liquid-helium surfaces. We monitor the gas during filling and decay by observing the atoms which are ejected from the trap as a result of spin exchange and magnetic dipolar relaxation. The stability of the gas is unaffected if we change the wall coverage from pure /sup 4/He to dilute /sup 3/He//sup 4/He mixtures. The maximum trapped density is 3 x 10/sup 14/cm/sup -3/ at about 100 mK. The limiting decay rate is attributed to dipolar relaxation and found to agree with theory for both magnitude and field dependence.
TL;DR: In this article, the average relaxation time τn for the normal mode process was insensitive to the polydispersity Mw/Mn, but the width of the loss curve reflecting the distribution of the relaxation times increased with mw/mn, and the slope of the double logarithmic plot of τn against Mw changed at the characteristic molecular weight Mc from 2.0 in the range Mw Mc.
Abstract: Dielectric relaxations in undiluted cis‐polyisoprene (cis‐PI) with narrow molecular‐weight distribution were investigated. The normal mode process due to fluctuation of the end‐to‐end distance and the segmental mode process due to the local segmental motions were observed. The average relaxation time τn for the normal mode process was insensitive to the polydispersity Mw/Mn, but the width of the loss curve reflecting the distribution of the relaxation times increased with Mw/Mn. The slope of the double logarithmic plot of τn against Mw changed at the characteristic molecular weight Mc from 2.0 in the range Mw Mc. It was found that although the half‐width is nearly independent of Mw, the tail of the loss curve in the high frequency side broadens with increasing Mw. This indicates that by entanglement effects the distribution of the relaxation time for the normal mode process changes slightly. The segmental mode is found to be almost independent of the molecular weight and the ...
TL;DR: In this paper, a time-domain light scattering study of acoustic and mountain modes in glycerol is reported by using light-scattering angles between 089° and 889°, a wide range of acoustic frequencies is sampled.
Abstract: A time‐domain light scattering study of acoustic and Mountain modes in glycerol is reported By using light‐scattering angles between 089° and 889°, a wide range of acoustic frequencies is sampled The data also yield information about time‐dependent density responses to stress and to heat (the latter is the time‐dependent thermal expansion) These responses are associated with the Mountain mode and provide additional information about structural relaxation dynamics A theoretical framework is presented which can treat these experiments as well as ultrasonics and specific heat spectroscopy The time or frequency dependences of the elastic modulus, heat capacity, and pressure response to temperature change are all accounted for and appear to be significant The experimental results are fit best with a distribution of relaxation times which is somewhat less asymmetric than a Cole–Davidson distribution The width of the distribution (on a logarithmic frequency scale) does not change significantly in the 20
TL;DR: In this paper, it was shown that the importance of the dipolar contribution depends strongly on the viscosity and metal ion, and that the relationship between geometry and the magnitude of the exchange interaction is needed in order to better understand the relationship of the bond pathway between the two paramagnetic centers.