Nuclear Quadrupole Relaxation Research Articles

The quadrupolar relaxation rate of liquid rubidium

The nuclear quadrupolar relaxation rate of 85Rb in liquid rubidium has been measured. The value obtained, 99+or-22 s-1, is much larger than recent theoretical estimates which range from 8.4 s-1 to 24.4 s-1. It is suggested that a major part of the difference between theory and experiment may be due to the potential used to represent the conduction electron charge density.

Nuclear quadrupolar relaxation by translational diffusion in solids. II. Numerical evaluation of the mean-field theory and application to transition-metal deuterides

For pt.I. see ibid., vol.15, p.5123 (1982). The method of Pade approximants is invoked to evaluate numerically the relaxation rate spectral densities corresponding to the three-particle function over a range of temperatures for diffusion by nearest-neighbour jumps on SC and FCC lattices. These results can be used in conjunction with the analogous two-particle quantities tabulated by Barton and Sholl (1980) for dipolar relaxation to obtain quadrupolar spin-lattice relaxation rates for diffusion of any concentration c of particles (except the monovacancy limit c to 1) in non-metallic crystals. By including the effects of conduction electron screening according to a free-electron model, the predictions of the mean-field theory are applied to the interpretation of spin-lattice relaxation data for deuterons in transition-metal deuterides. The importance of the three-particle probability function and conduction electron screening, as well as the isotope dependence of the diffusion coefficient, in determining the temperature of the relaxation rate maximum for the deuterides, relative to that for the corresponding hydrides, is demonstrated.

14N Nuclear Quadrupole Resonance and Relaxation in 2,5-Dimethylpyrazine–Evidence of Level Crossing between NQR and Tunnel Systems–

NQR frequencies and spin-lattice relaxation times ( T 1 ) have been measured from 4.2 to 262 K by the pulse method. The quadrupole coupling constant (4.795 MHz) and the asymmetry parameter (0.4964) at 4.2 K are compared with those in tetramethylpyrazine. The temperature dependence of T 1 shows peculiar behavior: Above 200 K, the fluctuation of the electric field gradient dominates the relaxation, and the activation energy ( E a ) of the molecular motion has a value of 55 ±5 kJ mol -1 . Below 100 K, T 1 is governed by dipolar interactions between 14 N and 1 H. T 1 minima are observed at 69 K and at 52 K. The methyl-group reorientation ( E a =6.5 kJ mol -1 ) contributes to T 1 (min) at 69 K, giving the pre-exponential factor of the correlation time, τ 0 =5 ×10 -13 s. T 1 (min) at 52 K is explained with the use of a tentative model of the level crossing between NQR and tunnel systems.

Nuclear relaxation, molecular motions and interactions. Part II. 14N nuclear quadrupole relaxation from the1H line-shape analysis, and viscosity measurements of pyrrole in “non-active” solvents

Abstract The 14N relaxation time of pyrrole in cyclohexane, carbon tetrachloride and pentafluororyridine solution has been determined at a number of temperatures through a line-shape analysis of the imido proton pmr signal of pyrrole (scalar relaxation of the second kind). The viscosity of pyrrole in the same solvents has also been measured. The results are discussed in terms of solvent effects on the association equilibria of pyrrole.

Molecular dynamic simulation of quadrupole relaxation of atomic ions in aqueous solution

Molecular dynamics (MD) simulations were performed in order to investigate the molecular origin of the nuclear quadrupole relaxation mechanism for Li+, Na+, and Cl− ions in dilute aqueous solution. Different boundary conditions were investigated in the simulations, but neither the boundary conditions nor the system size have any significant effect on the different time correlation functions (tcf:s) calculated. It is found that the field gradient tcf, determining the NMR relaxation rate for these ions, is almost completely due to the water molecules in the first shell. The calculated field gradient tcf:s show a complex time-dependence not describable with a mono-exponential decay. The very rapid decay shown by the field gradient tcf for all three ions can partly be attributed to a correlated water motion in the first hydration shell. The relaxation rates obtained from the simulations are in excellent agreement with experimental data for Na+ and Cl−, while the Li+ relaxation rate is less well produced.

Electric field gradient modulation and nuclear magnetic relaxation in hexacyanocobaltate ion

The 59Co, 15N, and 13C NMR relaxation rates are reported for potassium hexacyanocobaltate in aqueous solutions as a function of temperature and counter ion. The 59Co relaxation rate is dominated by the nuclear electric quadrupole relaxation mechanism, but measurements of the 13C and 15N relaxation rates show that modulation of the electric field gradient at the cobalt nucleus is not coupled to rotation of the symmetrical complex ion. The field gradient change at the cobalt nucleus resulting from ion-pair formation with magnesium ion is on the order of or less than 30%. This observation supports the hypothesis that larger changes in the relaxation rate of the central ion are due to perturbations in the first-coordination sphere of the observed ion.

Local degrees of freedom and nuclear quadrupolar spin relaxation in liquid metals and alloys

We discuss the temperature dependence of the nuclear quadrupolar spin relaxation rate in metals and alloys. Four different relaxation processes must be distinguished: Hard collisions, diffusion, decay of associates and rotational diffusion. The latter two processes are important in alloys of strongly interacting alloying partners, the former in pure metals (collision) and ideal or regular mixtures. Diffusion is important if the alloying partners produce different electrical field gradients.

Nuclear quadrupolar relaxation and the dynamics of pairs of atoms in liquids

We have developed a model calculation for the electrical field gradient correlation function on a probe atom in the liquid, cEFG(t)= . In this model, symmetry of the liquid is introduced explicitly and the distribution function for therelative coordinate ri(t) between the probe atom and particle i is calculated using Smoluchowski's diffusion equation with a mean force potential Φ(r)=kBT In g(r). The results for cEFG(t) can be characterized by two correlation times, Open image in new window , the shorter one being responsible for the small values of RQ in pure liquid metals, the longer one producing the increase of RQ in alloys. Also good agreement is found with recent results for cefg(t) from molecular dynamics studies.

Nuclear Quadrupolar Spin Relaxation and Association in Binary Liquid Metallic Alloys

AbstractWe present experimental data for the nuclear quadrupolar spin relaxation rate Rq in liquid InxSb1–x, HgxK1–x and In50Hg50. The results for the concentration and temperature dependence of Rq can be qualitatively interpreted with the framework of association in these systems (quasi ternary solution model). We conclude that the relaxation is mostly due to the decay of associates in HgIn and to rotational diffusion of associates in Hg – K. In In – Sb, the corresponding correlation times seem to be equal so that both relaxation processes may contribute to the relaxation. The analysis of microscopic experiments using the concept of association may prove useful for a better understanding of the nature of the associates.

Microscopic charge fluctuations in the liquid semiconducting alloys Ga-Te and In-Te

Measurements are presented of the nuclear quadrupolar spin relaxation rate on an inert probe atom, 123Xe (using the TDPAD technique), in GacTe1-c and IncTe1-c alloys. Despite the apparent similarities of these systems, the relaxation rate in In-Te alloys is larger than in Ga-Te alloys. A possible connection of this difference with a difference in bond type is discussed.

Nuclear quadrupolar relaxation and association in liquid InSb

A thermodynamic model of associates is applied to discuss the large increase of nuclear quadrupolar relaxation rate R Q found in many liquid alloys with compound-forming tendency, by considering the concentration and lifetime of associates. Data for concentration and temperature dependence of R Q of Sb in In 1- c Sb c are presented and explained by known thermodynami properties of the alloy; a characteristic time of the order of 10 −11 s is estimated.

Molecular reorientation of liquid trimethylchlorosilane from 13C, 29Si and 35 Cl FT NMR relaxation studies

13C and 29Si spin—lattice relaxation times and nuclear Overhauser enhancement factors and 35Cl quadrupole relaxation times of neat liquid

23Na nuclear magnetic resonance linewidth studies of sodium tetraethylaluminate: complexes with hexamethylphosphoramide in benzene

The linewidth of the 23Na resonance in sodium tetraethylaluminate in benzene has been measured as a function of the ratio of [donor]: [Na+] using the strong complexing agent hexamethylphosphoramide. In this system changes in the sodium linewidth arise primarily from changes in the nuclear quadrupole relaxation at the sodium nucleus which in turn arise from changes in the electric field gradient. As the ratio of hexamethylphosphoramide to sodium ion is increased up to 3: 1 the 23Na linewidth progressively decreases due to an increase in cation–anion distance in the ion pair. After a ratio of 4:1 is reached, essentially no linewidth change is noted, indicating a stable solvation number of 4 for hexamethylphosphoramide. The results of this study indicate that this is a new and promising approach to the determination of solvation numbers of the sodium ion.

14N nuclear quadrupole resonance and relaxation in tetramethylpyrazine

Resonance frequencies and spin–lattice relaxation times (T1) of nitrogen-14 nuclei in solid tetramethylpyrazine from liquid-helium temperature to room temperature have been measured by the pulse method and the temperature dependence of the quadrupole resonance frequencies is compared with those in the low-temperature phase of pyrazine. Below 150 K, the relaxation times are governed by the reorientation of the methyl groups. The activation energy and the pre-exponential factor of the correlation time are found to be Ea= 6.0 kJ mol–1 and τ0= 2 × 10–13 s, respectively. Above 150 K the relaxation times depend on torsional lattice vibrations and are determined by the indirect two-phonon processes so that T–11∝T2.

Nuclear quadrupolar relaxation by translational diffusion in solids: I. Mean field theory

The theory of nuclear quadrupolar relaxation due to translational diffusion in crystalline solids is investigated. Unlike the case of dipolar relaxation, it is often necessary to take into account three-particle, as well as two-particle, probability functions in the expression for the spectral densities of the quadrupolar interaction. In particular, the nuclear relaxation of a particle diffusing on a cubic lattice, due to the relative translational motion of other identical particles on the same lattice, is evaluated according to the mean field theory which includes, in an average way, the effects of spatial correlations between the motions of particles. Formal expressions are obtained for the three-particle probability function for nearest-neighbour jumps on SC, FCC and BCC lattices. Analytical formulae are derived for the spectral density functions in the low-temperature limit and demonstrate the greater importance of three-particle effects as the concentration of particles increases. In a subsequent paper, the mean field theory is applied to the quadrupolar relaxation of deuterons in transition metal deuterides.

ChemInform Abstract: NITROGEN‐14 NUCLEAR QUADRUPOLE RELAXATION IN N‐METHYLPIPERIDINE

Chemischer InformationsdienstVolume 13, Issue 18 Physical Organic Chemistry ChemInform Abstract: NITROGEN-14 NUCLEAR QUADRUPOLE RELAXATION IN N-METHYLPIPERIDINE H. NEGITA, H. NEGITASearch for more papers by this authorT. KUBO, T. KUBOSearch for more papers by this authorM. MAEKAWA, M. MAEKAWASearch for more papers by this author H. NEGITA, H. NEGITASearch for more papers by this authorT. KUBO, T. KUBOSearch for more papers by this authorM. MAEKAWA, M. MAEKAWASearch for more papers by this author First published: May 4, 1982 https://doi.org/10.1002/chin.198218052AboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue18May 4, 1982 RelatedInformation

Nuclear quadrupole relaxation in chlorates

Sodium, barium and silver chlorates have been subjected to NQR investigations, Measurements of the 35Cl pure quadrupole resonance frequency and relaxation times were carried out in the temperature range from 290 K to temperatures where the NQR signal vanishes. It was found, that temperature dependence of the T 1 indicates some activation processes. The hindered rotation of ClO 3 groups and the water diffusion are playing an essential role in the description of phenomena occuring in these crystals.

14N Nuclear Quadrupole Relaxation in N-Methylpiperidine

Abstract Two crystal modifications of N-methylpiperidine were found by means of the nuclear quadrupole resonance (NQR) of Nitrogen-14. From the temperature dependence of the 14N spin-lattice relaxation times (T1), it is deduced that the α-form has a lower activation energy for the reorientation of the methyl group than the β-form.

Probe atom dependence of nuclear quadrupolar relaxation in liquid alloys

Probe atom dependence of nuclear quadrupolar relaxation in liquid alloys

Angular Dependence of the Nuclear Quadrupole Relaxation Rate in Tantalum Due to Diffusing Hydrogen, Studied by Nuclear Acoustic Resonance (NAR)

Angular Dependence of the Nuclear Quadrupole Relaxation Rate in Tantalum Due to Diffusing Hydrogen, Studied by Nuclear Acoustic Resonance (NAR)