Dipolar Relaxation Time Research Articles

Cross relaxation dispersion and temperature dependence of nuclear spin dipolar and rotating frame Zeeman energies: A study of ammonium halides

The less known properties of cross relaxation between detectable spins I and fast relaxing spins S, such as the two types of H1 dispersion and the occurrence of two minima of the rotating frame Zeeman relaxation time T1x(I), when γH1T1(S)min<1, or the occurrence of two minima of the dipolar relaxation time T1d(I), when γHL, eff(I) T1(S)min<1 and T1(S)min≪T2(IS), are briefly discussed in the framework of the Blinc–Pirš–Žumer theory. The experimental results on cross relaxation between detectable spins I (protons or deuterons) and fast relaxation spins S (bromine, iodine, and chlorine) in the cubic phases of solid NH4Br, NH4I, and NH4Cl, and their deuterated analogs, are presented and explained.

High-temperature nuclear spin relaxation in51V metal: self-diffusion and interstitial-impurity diffusion effects

Zeeman and dipolar reservoir nuclear spin relaxation times T1Z, T1D and T2 in 51V metal have been measured in samples with different purities, over temperatures within the 300-1700K range. T1Z and T1D have been analysed into electronic, quadrupolar and diffusion contributions, whose temperature dependences have been determined. For the electronic contributions it has been shown that T1eZ=(2+ epsilon )T1eD with epsilon <0.05 which means that electron-density correlation effects are negligible. From the quadrupolar contribution to T1Z an activation energy value of (0.8+or-0.1) eV has been determined for interstitial oxygen migration around 1000K. From the diffusion contributions to T2 and T1D the authors have deduced a self-diffusion activation energy of (3.2+or-0.1) eV on the purest sample and values of the diffusion coefficients in the 1200-1600K temperature range which are in agreement with measurements made by radioactive tracers. This 3.2 eV value is attributed to a single-vacancy mechanism and it has been shown that interstitial oxygen increases the self-diffusion through extrinsic vacancies with lower activation energy values.

Molecular motion in liquid toluene and perfluorotoluene from carbon-13 spin-lattice relaxation measurements

Abstract Carbon-13 spin-lattice relaxation times and nuclear Overhauser enhancement factors are reported for neat toluene and octafluorotoluene at 301 K. A thorough analysis of the experimental data shows the overall reorientation of these molecules to be that of an axially symmetric ellipsoid, with diffusion coefficients D⊥ = 6.45 and and D// = 14.20 and respectively. The internal rotation of the attached methyl group is consistent with a 60° random jump model. The rotational barrier heights are of the same order of magnitude in both compounds : 5.1 and 6.1 kJ.mol−1, thus showing that the decreased mobility of the perfluoromethyl group in perfluorotoluene with respect to that of the methyl substituent in toluene should be traced to inertial and not to structural factors. The dipolar relaxation time of the substituted carbon atom C1 of toluene can be computed from these data and is shown to coincide with the experimental value within 4 % (349 and 363 s).

Erratum: “Concentration Dependence of Relaxation Time of Polarization Fluctuation in Mixed Crystals KDP1-xDKDPx”

Brillouin scattering spectra in the geometry x ( y , x ) y were measured in mixed crystals KDP 1- x DKDP x for x =0.04, 0.08, 0.23. 0.46 and 0.72. A spectrum consists of a broad component owing to polarization fluctuation and a phonon peak. On the assumption that polarization fluctuation is of Debye type, a relaxation time of an individual dipole is evaluated by fitting the calculated spectrum to an experimental one in a polarization fluctuation-acoustic phonon coupling system. The relaxation time increases from 0.19 ×10 -12 sec at x =0.04 to 1.03 ×10 -12 sec at x =0.72.

Molecular motions and phase transitions. NMR relaxation times studies of several lecithins

The spin-lattice relaxation time, T1, and the dipolar energy relaxation time, TD, were measured as a function of temperature. The materials studied were samples of anhydrous L-dipalmitoyl lecithin, DL-dipalmitoyl lecithin, L-dimyristoyl lecithin, DL-dimyristoyl lecithin and their monohydrates, and of anhydrous egg yolk lecithin. It is shown that TD is a much more sensitive parameter than T1 for the determination of the Chapman phase transition. Comparison between T1 and TD provides information about new types of slow molecular motions below and above the phase transition temperature. It is suggested that the relaxation mechanisms for T1 and TD in the gel phase are governed by segmental motion in the phospholipid molecule. A new metastable phase was detected in dimyristoyl lecithin monohydrates. This phase could only be detected from the dipolar energy relaxation times.

Concentration Dependence of Relaxation Time of Polarization Fluctuation in Mixed Crystals KDP1-xDKDPx

Brillouin scattering spectra in the geometry x ( y , x ) y were measured in mixed crystals KDP 1- x DKDP x for x =0.04, 0.08, 0.23. 0.46 and 0.72. A spectrum consists of a broad component owing to polarization fluctuation and a phonon peak. On the assumption that polarization fluctuation is of Debye type, a relaxation time of an individual dipole is evaluated by fitting the calculated spectrum to an experimental one in a polarization fluctuation-acoustic phonon coupling system. The relaxation time increases from 0.19 ×10 -12 sec at x =0.04 to 1.03 ×10 -12 sec at x =0.72.

Light Scattering Spectra of a Polarization Relaxational Mode-Acoustic Phonon Coupled System

Light scattering spectra are theoretically studied near the transition temperature in a polarization relaxational mode-acoustic phonon coupled system. It is algebraically shown that qualitatively different temperature dependences of the spectra are attributed to the difference of the magnitude of the parameter z 0 introduced by Levanyuk and Sobyanin; the parameter z 0 is proportional to the square of the coupling constant divided by the product of the relaxation time of an individual dipole and the cube of the frequency of the acoustic phonon. The temperature dependences of the spectra for several scattering geometries are numerically calculated in KH 2(1- x ) D 2 x PO 4 mixed crystals on the basis of available experimental data. The numerical results accord with the algebraic predictions and simulate well the observed spectra.

Temperature dependences of light scattering spectra in mixed crystals KH 2(1−x)D 2xPO 4

The light scattering spectra in KH 2(1−xD 2xPO 4 mixed crystal are measured above the transition temperature. The results are analyzed on the basis of the model consisting of a dipole relaxational mode and an acoustic shear mode. It is shown with this model that qualitatively different temperature dependences of the spectra can be derived by varying the relaxation time of an individual dipole within an order of magnitude. This theoretical prediction is found to be in good agreement with the observed spectra in the mixed crystals.

A theoretical approach to the dielectric relaxation of liquid alcohols

The dielectric relaxation mechanism of liquid alcohols was studied by assuming the association equilibrium between hydrogen-bonded chain multimers. The dipole inversion arising from the cooperative rotation of the OH groups of the multimers was considered to be the main mechanism of the dipole relaxation. The stochastic model of one-dimensional random walk was introduced to explain the dipole inversion process and it was found that the dipole relaxation time of an n-mer is proportional to n+1. Based on this result and the stoichiometry of the association equilibrium, we calculated the dielectric constants and losses of liquid alcohols as a function of ω, which are in fair agreement with the experimental results.

A high field proton magnetic resonance study of the solution conformation of thromboxane B2

The solution conformation of thromboxane B2 (TXB2) has been studied using high-field nuclear magnetic resonance techniques. In CDCl3, both anomers are present in solution with 76% 11α-OH TXB2 and 24% 11β-OH TXB2. In CD3OD, the predominant anomer is 11β-OH TXB2 (80%) while the concentration of 11α-OH TXB2 is 20%. The proton resonances were assigned at 400 MHz using double resonance techniques. The analysis of the vicinal coupling constants indicates that the six-membered ring is present in solution in a chair conformation with both of the aliphatic side chains equatorial. Proton longitudinal relaxation times were measured at 25 °C in CDCl3 for H-2, H-11β, H-12, H-13, H-14, and H-17 to H-19, both at 200 MHz and at 400 MHz. From the frequency dependence of these dipolar relaxation times, the rotational correlation times were evaluated. Within experimental error, all of the values are similar in magnitude (~ 2.0 × 10−10 s) indicating that this is the molecular rotational correlation time.

Measurement of short dipolar relaxation times by the saturation method

The dipolar order, created by off-resonance of irradiation, is observed on-resonance after switching in less than 1 μsec with the help of a digital switch. The measurements have been done on the protons of ND + 3CHCH 3COOO − powder at room temperature. It is found that the observed signal is rather constant during the first 100 μsec, in contrast to that obtained by the pulse method. The values of the relaxation time obtained by both methods are the same, namely, 22 +- 1 msec.

Dielectric and NMR studies of the molecular movements in comb-like polyfluoro-alkyl acrylates and polyfluoro-alkyl methacrylates

The characteristics of the molecular movements have been studied in a series of polyacrylate and polymethacrylate homologues containing fluoro-alkyl fragments in the branches. The ability of the secondary groups to arrange themselves in an orderly fashion and to crystallize has been shown to apply to the lower homologues; the transition to the highly-elastic state and the melting have shifted into higher temperature ranges when compared with those of the polyalkyl acrylates (PAA) and polyalkyl methacrylates (PAMA). Relaxation processes due to the mobilities of the ester and the polar end groups in the branches, the α-methyl groups, and also the fluoromethylene fragments, have been detected at low temperatures. The comb-like homologues in the series with differing compositions have been found to have dipolar polarization relaxation times of the ester groups at low temperatures which depend to a large extent on the interactions and the arrangement of the side chains.

On the dynamics of the pseudo one-dimensional ferroelectric ordering in CsH2PO4and CsD2PO4

Abstract Measurements of the temperature dependence of the phosphorus Zeeman and dipolar spin-lattice relaxation times in CsH2PO4 show in the temperature range dominated by one-dimensional correlations an extremely strong dynamic central peak which decreases by four orders of magnitude on going to the range dominated by three dimensional correlations. The order fluctuation spectrum is qualitatively different in the case of CsD2PO4.

Dipolar relaxation times and signal assignment in 13C NMR spectra of 2-substituted adamantanes

It is shown that by correlating measured dipolar relaxation times with the theory of dipolar nuclear relaxation developed by Woessner and Huntress it is possible to assign NMR signals of a substance that, by other methods, cannot be differentiated in a similarly simple way. As an example, the relaxation times of 2-substituted adamantanes have been measured and the signals of the δ s and γ a atoms have been assigned.

19F N.M.R. and127I N.M.R. and N.Q.R. study of the molecular motions and deformations of iodine heptafluoride in its solid phases

In solid IF7, 19F and 127I N.M.R. and 127I N.Q.R. absorption line shapes, frequencies and relaxation times have been studied from the melting temperature down to 56 K. Two new solid-solid transitions have been found at 180 K and 96 K in addition to the one already known at 153 K. The two high temperature phases are shown to be plastic. The fast molecular rotations and the slow molecular diffusion are studied from 19F and 127I relaxation times. In the ordered phases, an analysis of the 19F second moments and longitudinal relaxation times shows the existence of a fast intramolecular exchange between axial and equatorial fluorine atoms, together with a much faster reorientation about the D 5 axis. The characteristic times of these two motions are obtained and a mechanism for the exchange process is proposed. The chemical shift values of 127I, the temperature dependence of the N.Q.R. frequencies and of the N.Q.R. relaxation times of 127I, as well as the dipolar energy relaxation times have been measured and are discussed.

Resonant transfer of the nuclear spin dipolar order in the rotating frame

A method for transferring the nuclear spin dipolar energy in a solid lattice is presented. It is shown that order may be transferred between the Zeeman and nuclear spin dipolar systems in either direction by rf pulses of suitable amplitude. This method may also be used to measure the dipolar relaxation time. Experimental data on ammonium chloride are shown to be in close agreement with the theory.

AnomalousH1spin-lattice relaxation in antiferroelectric ammonium dihydrogen phosphate (ADP)

$^{1}\mathrm{H}$ NMR static, and rotating-frame spin-lattice relaxation times and dipolar relaxation times were measured between 135 and 270 K for a single crystal of ammonium dihydrogen phosphate. Random fluctuation in nuclear dipolar interactions by means of ammonium-ion reorientation was found to be the dominant relaxation process. A critical fluctuation contribution to relaxation near the paraelectric-antiferroelectric phase transition, which was postulated in a previous study, was found to be unnecessary to account for the relaxation-time results.

NMR investigation of the layered transition metal phosphorus trichalcogenides and the intercalation compounds Li xNiPS 3

The transition metal phosphorus trichalcogenides MPX 3 are layered semiconductors which can be intercalated either chemically or electrochemically by lithium atoms. We present a NMR study of the magnetic properties of the MPX 3 compounds (M = Ni, Mn, Fe; X = S, Se) and their modification as a function of intercalation in the compounds Li xNiPS 3 (x = 0 − 1.29). In the concentration range x = 0.02 − 0.5, the relative shift of the P 31 resonance line K iso = -0.052 % and the Neel temperature T N = 155 K are constant and barely different from that measured in pure NiPS 3 ( K iso = -0.057 %, T N = 165 K). For x > 0.5 a new P 31 resonance line is observed, which grows with x at the expense of the previous one. It corresponds to non magnetic layers S - Ni 2 3 (P 2) 1 3 - S , which progressively replace the paramagnetic ones up to the limit of intercalation x = 1.29. Investigation of the lithium ions mobility through Zeeman and dipolar spin lattice relaxation times T 1∼ and T 1D measurements indicates a very low self-diffusion coefficient - D = 10 -13 − 10 -14 cm s -1 -, that is four orders of magnitude smaller than those measured in Li xTiS 2 compounds. This strongly contrasts with the good electrochemical activity of the Li xNiPS 3 system.

Nuclear-magnetic-resonance methods for identifying and studying diffusion of different spin species in heteronuclear systems

We introduce a new dipolar relaxation time ${{T}_{1D}}^{\ensuremath{'}}$ which characterizes the spin-lattice relaxation of secular dipolar interactions in the presence of a large rf field. Measurements of ${{T}_{1D}}^{\ensuremath{'}}$ are particularly useful for studying slow atomic motions in multispin systems, since such measurements enable us to vary the contribution of a particular spin species's motion relative to the contribution of the other spin species's, thus enabling us to identify the diffusing species. We also show that the anisotropy of the conventional dipolar relaxation time ${T}_{1D}$ can differ enormously for diffusion of different spin species in a multispin system and, accordingly, can be used to identify the dominant diffusing species. Finally, we show that the high-rf-field rotating-frame relaxation time ${T}_{1\ensuremath{\rho}}$, measured as a function of rf frequency, also enables us to identify the diffusing species. We demonstrated experimentally the validity of these techniques by measurements of potassium vacancy diffusion in a KF: ${\mathrm{Ca}}^{++}$ single crystal and measurements of fluorine diffusion in AgF powder.

ChemInform Abstract: STUDIES ON THE DIPOLE MOMENTS AND RELAXATION TIMES OF COPPER(II) STEARATE IN BENZENE SOLUTION

Chemischer InformationsdienstVolume 9, Issue 1 Physical Organic Chemistry ChemInform Abstract: STUDIES ON THE DIPOLE MOMENTS AND RELAXATION TIMES OF COPPER(II) STEARATE IN BENZENE SOLUTION L. PARDESHI, L. PARDESHISearch for more papers by this authorR. A. BHOBE, R. A. BHOBESearch for more papers by this author L. PARDESHI, L. PARDESHISearch for more papers by this authorR. A. BHOBE, R. A. BHOBESearch for more papers by this author First published: January 3, 1978 https://doi.org/10.1002/chin.197801053AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume9, Issue1January 3, 1978 RelatedInformation