Showing papers on "Relaxation (NMR) published in 1975"
TL;DR: In this article, a model based on semiclassical collision theory is presented to describe the dephasing of vibrationally excited molecules in a liquid, and it is shown that fluctuations of the vibrational frequencies which are caused by the intermolecular interaction, lead to phase relaxation of a coherently excited state.
369 citations
TL;DR: In this article, the effect of the magnetic dipolar interaction of a nuclear spin with the thermal average of an electronic spin (Curie spin) is modulated by molecular motion but not by the electronic spin relaxation.
308 citations
TL;DR: In this paper, a detailed analysis of line shapes and relaxation is made for the perdeuterated 2,2,6,6-tetramethyl-4-piperidone Noxide (PD-Tempone) nitroxide radical covering the whole range from fast motional narrowing (TR - 10-12 sec) to the rigid limit (TR − 10-6 sec) in several deuterated solvents.
Abstract: A detailed analysis of line shapes and relaxation is made for the perdeuterated 2,2,6,6-tetramethyl-4-piperidone N-oxide (PD-Tempone) nitroxide radical covering the whole range from fast motional narrowing ( TR - 10-12 sec) to the rigid limit (TR - 10-6 sec) in several deuterated solvents. The slow tumbling results show particularly good agreement with the slow tumbling theory of Freed, et al., for a reorientational model of moderate jumps (ca. 50° rrns), and essentially isotropic reorientation. It is shown that while such a model may not be readily distinguished, purely from its slow tumbling spectral predictions, from a free diffusion model including inertial effects, the latter model is incompatible with most other considerations. However, a simple analysis explicitly including the fluctuating (or random) torques indicates that more fundamental analysis of the dynamics may explain the slow tumbling results without necessarily involving substantial jumps. The spectral analysis is considerably enhanced by the increased resolution obtained from the use of the perdeuterated spin probe and deuterated solvents. Careful analysis of results at X-band and 35 GHz has shown that the nonsecular spectral densities exhibit significant deviations from a Debyelike spectral density yielding results very similar to those recently reported for the peroxylaminedisulfonate (PADS) radical. Related observations are discussed of apparent non-Debye-like spectral densities in the incipient slow tumbling spectra. These anomalies are also found to be amenable to a unified explanation in terms of the fluctuating torques. The analysis of much of the results in terms of a simple model yields an rms value for the fluctuating torques of ca. AT and TM - TR where TM is the relaxation time of the torques. The high-temperature electron-spin flip processes are consistent with a Hubbard-type spinrotational mechanism, but the low-temperature results may be due to spin-rotational relaxation from intramolecular motions. The simple analysis of spin-rotational relaxation in terms of relaxation of the fluctuating torques is found to yield equivalent predictions to conventional treatments when the estimated values of rms torque and TM are used.
277 citations
188 citations
TL;DR: In this paper, the equations for steady isothermal spinning of a viscoelastic liquid were solved for a fluid model with constant modulus and a single constant relaxation time, and high stress levels are predicted for elastic liquids, and the velocity approaches a linear profile in the limit of maximum drawdown.
Abstract: The equations for steady isothermal spinning of a viscoelastic liquid are solved for a fluid model with constant modulus and a single constant relaxation time. High stress levels are predicted for elastic liquids, and the velocity approaches a linear profile in the limit of maximum drawdown. These predictions are in accordance with the observed behavior of polymeric liquids in isothermal spinning. Relaxation times computed from spinning data of Spearot and Metzner and Acierno et al. for four low density polyethylene melts are comparable to those measured rheogoniometrically, though the spinning relaxation times are 20 to 80% larger.
157 citations
156 citations
TL;DR: In this paper, a theroy relating rotational Brownian motion to the time autocorrelation function of the intensity of radiation from a fluorescent system composed of spherical rotors is presented.
Abstract: A theroy relating rotational Brownian motion to the time autocorrelation function of the intensity of radiation from a fluorescent system composed of spherical rotors is presented. The calculation shows three relaxation times, two associated with the rotational diffusion, and the third associated with the natural decay of the fluorescence. The correlation function contains terms that relax independently of the fluorescence decay time, thus arbitrarily extending the time range over which rotational diffusion can be studied by fluorescence.
140 citations
TL;DR: In this paper, the effect of protein size on 13C NMR NMR spectra was evaluated by comparing the 13C-1H dipolar mechanism and the nuclear Overhauser enhancements (NOE).
139 citations
137 citations
TL;DR: In this article, a theory of dielectric relaxation is presented which relates the frequency-dependent Dielectric constant to a truly single-particle correlation function, and the correlation function is shown to have the same form as, and to be related to, a true single particle correlation function; this relationship is proved in limited form elsewhere but generalized here.
Abstract: A theory of dielectric relaxation is presented which relates the frequency-dependent dielectric constant to a truly single-particle correlation function. For a sample of suitable geometry, linear response theory is used to relate the polarization to a many-particle correlation function. This correlation function is shown to have the same form as, and to be related to, a true single-particle correlation function; this relationship, proved in limited form elsewhere but generalized here, is the principal result of this work. This contrasts with the usual method of obtaining ‘ small ’ macroscopic correlation functions by reducing the sample dimension until it contains but a single particle, assuming all along that macroscopic dielectric theory is applicable. We are thus able to devise a relationship between the single-particle relaxation time and the observed many-particle relaxation time which will enable the dielectric relaxation data to be compared with reorientational relaxation times obtained in other ex...
118 citations
TL;DR: In this paper, the effect of the degree of localization of the hole state on the relaxation energies in metals is discussed and shown to be small. But it is argued that valence-band spectra obtained by different methods can be compared most directly among states with the same number of core holes.
Abstract: X-ray photoemission experiments were performed on samples of magnesium and aluminum prepared with clear surfaces in ultrahigh vacuum. Core-level binding energies were in excellent agreement with x-ray emission data. Asymmetries in core-level peaks were observed and are compared with theory. The Mg KLL Auger spectrum showed kinetic energies higher than the literature values. Many-body effects, in the form of extra-atomic relaxation, were present in core levels and Auger lines. Both KL/sub i/V and KL$sub 2$,$sub 3$V Auger peaks of Mg were observed. Many-body effects were also manifest as rich plasmon satellite structure accompanying every primary peak. The valence-band spectrum was compared with x-ray emission data and with the KL$sub 2$,$sub 3$V peak. The spectra were interpreted in terms of energy-level diagrams rather than one- electron levels. It is argued that valence-band spectra obtained by different methods can be compared most directly among states with the same number of core holes. A hierarchical classification of hole states is suggested. The effect of the degree of localization of the hole state on the relaxation energies in metals is discussed and shown to be small. It was observed that in several light metals the energies required to remove a valence-bond electron or amore » unipositive ion core are about equal. (auth)« less
TL;DR: In this article, the authors considered the case that reorientation of a molecule at time t ⪢ 0 may be due not only to the nearest defect at t = 0, but to any defect in the liquid, and concluded that a model of dielectric relaxation by diffusion of defects only leads to considerable deviations from a single relaxation time when the diffusion is restricted in some way.
TL;DR: In this article, a general type of electron-nuclear-nuclear TRIPLE resonance was performed on radicals in liquid solution, where two inequivalent nuclei were irradiated simultaneously at their respective NMR frequencies, the resonance being detected by an enhancement of a saturated ESR line.
Abstract: For the first time a general type of electron–nuclear–nuclear TRIPLE resonance has been performed on radicals in liquid solution. In this method two inequivalent nuclei are irradiated simultaneously at their respective NMR frequencies, the resonance being detected by an enhancement of a saturated ESR line. This general TRIPLE experiment, the analog of which is known already in the solid state (DOUBLE ENDOR), gives direct information about relative signs of hyperfine coupling constants. Several important aspects of the experimental setup are described. The experimental results are discussed on the basis of a simple relaxation model.
TL;DR: Water exchange between human red blood cells and the plasma phase was measured by water proton nuclear magnetic resonance relaxation in the presence of low concentrations of Mn( II) and by 17O relaxation of H217O in the absence of added Mn(II).
TL;DR: Theoretical studies of rotational relaxation in para-hydrogen are presented in this paper, where rotational energy relaxation rates extracted from these calculations are compared with available experimental data and are shown to be in good qualitative agreement.
Abstract: Theoretical studies of rotational relaxation in para‐hydrogen are presented. By using a set of theoretically deduced state‐to‐state rotational rate constants the master kinetic equations and the relevant fluid mechanical equations are solved numerically. Calculations are performed over the range 100⩽T⩽1100 °K to simulate conditions for free jet expansion, shock tube, and sound absorption experiments. The over‐all rotational energy relaxation rates extracted from these calculations are compared with available experimental data and are shown to be in good qualitative agreement. The magnitudes and the temperature dependence of these rates depend critically on the degree and direction of the initial departure from equilibrium as well as the multilevel nature of the relaxation process. The apparent discrepancies in the measured rates from the different experiments are shown to be qualitatively self‐consistent in light of the present calculations.
TL;DR: In this paper, Tinti et al. observed a radiative transition within the A 2 Σ+ state of OH and OD in a Ne lattice at 4.2 ǫ°K.
Abstract: Radiationless transitions within the A 2Σ+ state of OH and OD in a Ne lattice at 4.2 °K are observed. The radicals are substitutional impurities undergoing slightly perturbed free rotation [D. S. Tinti, J. Chem. Phys. 48, 1459 (1968)]. The local phonon relaxation time is ?10 nsec. Emission spectra show an intermediate strong coupling (or resonant mixing) occurring between rotational levels and lattice phonon levels. The v′=0 lifetimes are 582±10 and 565±10 nsec on OH and OD, respectively, with fluorescence quantum yields ≳0.90. The Lorentz–Lorenz dielectric model overestimates the vacuum to solid radiative rate increase by a factor of two. At high radical concentrations Forster transfer from OD(v′=0) to OH(v′=0) occurs. The vibrational relaxation rates are fast (4×104–4×105 sec−1), with higher rates in OH despite the larger vibrational energy gaps in OH. The rates are extremely sensitive to lattice defects and/or additional impurities causing small (?0.3 A) red or blue shifts from the principal site spect...
TL;DR: In this paper, 12 trimethylsilyl compounds have been studied by 29 Si and 13 C NMR data for chemical shifts, coupling constants, and spin-lattice relaxation times are reported.
TL;DR: In this paper, the infinite-temperature space and time-dependent spin-correlation functions of the infinite chain were studied for the one-dimensional (1, 2, 3, 4, 5, 7, 9) model.
Abstract: The infinite-temperature space- and time-dependent spin-correlation functions ${g}_{r}^{x}(t)$ are studied for the one-dimensional $\mathrm{XY}$ model. Numerical calculations are performed to obtain the exact autocorrelation function ${g}_{0}^{x}(t)$ for chains containing 5, 7, and 9 spins ($S=\frac{1}{2}$). This yields exact results for the first 16 moments of the frequency autocorrelation function of the infinite chain, and estimates for a few of the higher moments as well. The analysis suggests that ${g}_{0}^{x}(t)$ for the infinite chain is identical to $\frac{\mathrm{exp}(\ensuremath{-}{J}^{2}{t}^{2})}{4}$. We show that ${g}_{r}^{x}(t)$ for $r\ensuremath{
e}0$ vanishes identically for all values of time, implying a wave-vector-independent relaxation shape function. Our result for ${g}_{0}^{x}(t)$ is compared with that obtained by Huber for the classical ($S=\ensuremath{\infty}$) chain.
TL;DR: It appears that the protein molecules influence the dynamics of the motion of solvent water molecules in their neighborhood in a manner that imposes on all the solvent molecules a correlation time for their orientational relaxation which equals that of the solute proteins.
Abstract: Previous studies of the magnetic field dependence of the magnetic relaxation rate of solvent protons in protein solutions have indicated that this dependence (called relaxation dispersion) is related to the rotational Brownian motion of the solute proteins. In particular, the dispersion of the longitudinal (spin-lattice) relaxation rate 1/T1 shows a monotonic decrease with increasing field, with an inflection point corresponding to a proton Larmor frequency which is inversely proportional to the orientational relaxation time of the protein. We have now compared the relaxation dispersion of solvent 1H, 2H, and 17O In aqueous solutions of lysozyme (molecular weight 14,700) and 1H and 2H in solutions of hemocyanin (molecular weight 14,7 00) and 1H and 2H in solutions of hemocyanin (molecular weight 9 x 10(6)). The main experimental observation is that the dispersion of the relaxation rates of the three solvent nuclei in lysozyme solutions, normalized to their respective rates in pure water, is essentially the same. This is also true for 1H and 2H relaxation in hemocyanin solutions. These results confirm that entire solvent water molecules, rather than exchanging protons, are involved in the interaction. We have been unable to deduce the correct mechanism to explain the data, but we can eliminate several interaction mechanisms from consideration. For example, all observations combined cannot be explained by a simple two-site model of exchange, in which water molecules are either in sites on the protein with a relaxation rate characteristic of these sites, or else in the bulk solvent (the observed relaxation rate being the weighted average of the two). Also eliminated is the class of models in which the protein molecules induce a preferential partial alignment of neighboring solvent molecules, for example by electrostatic interaction of the electric dipole moments of the water with the electric fields produced by surface charges of the protein molecules. In addition, the idea that relaxation of solvent nuclei is due, in the main, to interactions with protein protons is precluded. Rather, it appears that the protein molecules influence the dynamics of the motion of solvent water molecules in their neighborhood in a manner that imposes on all the solvent molecules a correlation time for their orientational relaxation which equals that of the solute proteins.
TL;DR: In this paper, two chemically shifted resonances, separated by ∼015 ppm, arise from phosphate groups in phospholipid molecules on the inside and the outside of the spherical bilayer vesicles.
TL;DR: In this paper, it is argued that the increase of the paramagnetic resonance linewidth of CrBr3 with increasing temperatures above 100°K is primarily due to a spin-lattice relaxation mechanism.
TL;DR: In this paper, the effects of diluent on molecular motions and glass transition in the polystyrene-toluene system was studied by means of dielectric, thermal, and NMR measurements.
Abstract: The effects of diluent on molecular motions and glass transition in the polystyrene–toluene system was studied by means of dielectric, thermal, and NMR measurements. Three dielectric relaxations were observed between 80 and 400°K. On the basis of NMR measurements on solutions in toluene and in deuterated toluene, relaxation processes were assigned to segmental motions of polystyrene, rotations of toluene, and the local motions of polystyrene and toluene in order of appearance from the high-temperature side. The concentration dependence of the relaxation strength and of the activation energy for the primary relaxation (that at the highest temperature) show a step increment at about 50% by weight. The activation plots for the primary process were expressed by the Vogel–Tamman equation. With this equation, the temperatures at which the mean dielectric relaxation time becomes 100 sec is determined. This agrees well with the glass-transition temperature Tg and hence Tg in concentrated solution is expressed by
in terms of the parameters A, B, and T0 of the Vogel–Tamman equation. The values of A and B are, respectively, about 12 and 0.65 and independent of the concentration. The physical meaning of these parameters is discussed.
TL;DR: In this article, bond orientation correlation and autocorrelation functions are explicitly calculated for the case where only three-bond elementary motions are considered and effects due to the chain end are analyzed and the relaxation time distribution function is established.
Abstract: In the preceding paper, general equations were established for the motions of chains confined to a tetrahedral lattice. In the present paper, bond orientation correlation and autocorrelation functions are explicitly calculated for the case where only three-bond elementary motions are considered. Effects due to the chain end are analyzed and the relaxation time distribution function is established. The expressions obtained reflect the influence of the chain structure. Finally, to characterize the dynamic behavior of chains in orientation relaxation experiments, the notion of an independent kinetic segment is proposed.
TL;DR: The longitudinal relaxation of 17O in erythrocyte suspensions was non-exponential, reflecting water exchange across the cell membranes as well as relaxation processes inside and outside the cell, consistent with the thesis that hemoglobin modifies the NMR relaxation behavior of water inside cells and in free solution in the same way.
TL;DR: In this paper, the T1 values of 13C spin-lattice relaxation times T1 as structural parameters have been used for structural properties of a molecule, such as whether the molecular motion is anisotropic in solution, whether the internal motion of groups is subject to steric hindrance, and the extent to which strong intermolecular or interionic interactions affect the flexibility of the molecule.
Abstract: While the chemical shifts and coupling constants of 13C NMR belong to the most powerful tools available to the organic chemist for the solution of structural problems, increasing interest is being shown in 13C spin-lattice relaxation times T1 as structural parameters. Together with the nuclear Overhauser effects arising by proton decoupling of 13C NMR spectra, the T1 values of 13C nuclei in a molecule permit conclusions to be drawn with regard to relaxation mechanisms. They reflect the inter- and intramolecular mobility of a molecule, and thus complement the results of temperature-dependent NMR spectroscopy. The T1 differences within a molecule show, for instance, whether the molecular motion is anisotropic in solution, whether the internal motion of groups is subject to steric hindrance, the extent to which strong intermolecular or interionic interactions affect the flexibility of the molecule, and which parts of the molecule are rigid and which are flexible. Finally, differences between the T1 values measured for the 13C nuclei of a molecule frequently provide a reliable aid in the assignment of 13C NMR spectra, particularly in cases of signal crowding and multiplet overlapping.
TL;DR: In this paper, a method for measuring the distribution of dipolar relaxation times and the dielectric constants by thermally stimulated current (TSC) is described, where a technique of "thermal sampling" is used to isolate the TSC due to dipoles with a single relaxation time from the TCS due to Dipoles with distributed relaxation times, and a theory is developed to calculate distributions of the relaxation times from TSC measured by the thermal sampling.
Abstract: A method for measuring the distribution of dipolar relaxation times and the dielectric constants by thermally stimulated current (TSC) is described. A technique of ’’thermal sampling’’ is used to isolate the TSC due to dipoles with a single relaxation time from the TSC due to dipoles with distributed relaxation times. A theory is developed to calculate distributions of the relaxation times from the TSC measured by the thermal sampling. Dielectric loss factors in polyethylene terephthalate are calculated from the TSC data and they are compared with the experimental values of the dielectric loss factors obtained from the absorption current measurement.
TL;DR: In this article, Raman and infrared band shapes of some symmetric top molecules in the neat liquid and in solution were measured and used to obtain vibrational and rotational correlation functions and relaxation times.
TL;DR: In this article, the influence of multispin dipolar cross correlation effects is shown to influence the decoupled inversion-recovery experiment and lead to a predicted biexponential recovery of the carbon magnetization.
Abstract: The transient behavior of the carbon magnetization in proton decoupled spectra is discussed in detail for 13CH2 and 13CH3 spin systems. The influence of multispin dipolar cross correlation effects is shown to influence the decoupled inversion‐recovery experiment and lead to a predicted biexponential recovery of the carbon magnetization. It is rationalized that for methyl relaxation, the interference effects will play an inconsequential role. However, in the methylene case, it is demonstrated that there may arise many possible instances when it will become necessary to consider these correlation effects in much greater detail. It is also shown that if (1) extreme narrowing arguments are invalid or (2) other relaxation mechanisms compete with dipolar interactions, then the NOE enhancement factors deviate from those predicted from conventional treatments. For many conceivable situations, the inferred relaxation rate will underestimate the sum of the dipolar and nondipolar contributions whereas the usage of O...
TL;DR: In this paper, the vibrational relaxation of H2O by He, He, Ar, and N2 has been studied behind incident shock waves at temperatures between 1800 and 4100°K.
Abstract: The vibrational relaxation of H2O by H2O, He, Ar, and N2 has been studied behind incident shock waves at temperatures between 1800 and 4100°K. The relaxation processes were monitored by the observation of the infrared emission of the water vapor at 6.3 μ (the bending mode) and 2.7 μ (the asymmetric mode). The relaxation times for the two modes were found to be essentially the same with little temperature dependence. This implies rapid intramolecular energy transfer between the various modes. Measured values of pτ are 7.6×10−3, 0.23, 0.49, and 0.69 μsec⋅atm, respectively, for H2O−H2O, H2O−He, H2O−Ar, and H2O−N2 collisions.