Physical State of di-Nitrogen in the Presence of SBA and Various Zeolites Probed by 15N Spin–Lattice Relaxation of Pure 15N2 in the 30–300 K Temperature Range

2014 ◽  
Vol 118 (9) ◽  
pp. 4741-4750
Author(s):  
Jacques Fraissard ◽  
Sébastien Leclerc ◽  
William Conner ◽  
Daniel Canet
Keyword(s):  
Physical State ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Range ◽  
Spin Lattice

NQR Relaxation Studies on Halogenomethyl Groups in Halogenoacetates

1998 ◽  
Vol 53 (6-7) ◽  
pp. 480-483 ◽  
Author(s):  
Maria Zdanowska-Fnjczek
Keyword(s):  
Room Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Effect Of Temperature ◽  
Relaxation Theory ◽  
Temperature Range ◽  
Spin Lattice ◽  
Relaxation Studies

Abstract The effect of temperature on the chlorine NQR spin-lattice relaxation times in CsH(ClH2-CCOO)2 , KH(Cl3 CCOO) 2 and N(CH3)4 H(ClF2CCOO)2 has been studied in the temperature range 77 K to room temperature. The results were discussed on the basis of NQR relaxation theory.

scholarly journals The physical state of osmoregulatory solutes in unicellular algae. A natural-abundance carbon-13 nuclear-magnetic-resonance relaxation study

1982 ◽  
Vol 202 (3) ◽  
pp. 699-706 ◽  
Author(s):  
R S Norton ◽  
M A MacKay ◽  
L J Borowitzka
Keyword(s):  
Aqueous Solution ◽  
Green Alga ◽  
Physical State ◽  
Lattice Relaxation ◽  
Natural Abundance ◽  
Spin Lattice Relaxation ◽  
Paramagnetic Species ◽  
Intact Cells ◽  
Spin Lattice ◽  
Synechococcus Sp

Natural-abundance 13C n.m.r. spin-lattice relaxation-time measurements have been carried out on intact cells of the unicellular blue-green alga Synechococcus sp. and the unicellular green alga Dunaliella salina, with the aim of characterizing the environments of the organic osmoregulatory solutes in these salt-tolerant organisms. In Synechococcus sp., all of the major organic osmoregulatory solute, 2-O-alpha-D-glucopyranosylglycerol, is visible in spectra of intact cells. Its rotational motion in the cell is slower by a factor of approx. 2.4 than in aqueous solution, but the molecule is still freely mobile and therefore able to contribute to the osmotic balance. In D. salina, only about 60% of the osmoregulatory solute glycerol is visible in spectra of intact cells. The rotational mobility of this observable fraction is approximately half that found in aqueous solution, but the data also indicate that there is a significant concentration of some paramagnetic species in D. salina which contributes to the overall spin-lattice relaxation of the glycerol carbon atoms. The non-observable fraction, which must correspond to glycerol molecules that have very broad 13C resonances and that are in slow exchange with bulk glycerol, has not been properly characterized as yet, but may represent glycerol in the chloroplast. The implications of these findings in relation to the physical state of the cytoplasm and the mechanism of osmoregulation in these cells are discussed.

scholarly journals Nuclear quadrupolar spin-lattice relaxation with realistic phonon density of states in alkali halides

2017 ◽  
Vol 95 (11) ◽  
pp. 1042-1048 ◽  
Author(s):  
Ali Chandoul
Keyword(s):  
Temperature Dependence ◽  
Density Of States ◽  
Alkali Halides ◽  
Lattice Relaxation ◽  
Debye Model ◽  
Spin Lattice Relaxation ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Temperature Range ◽  
Spin Lattice

The nuclear quadrupolar spin-lattice relaxation times T1 have been calculated in alkali halides, whereby the phonon densities of states have been extracted from the shell model lattice dynamics. The calculations at room temperature were performed on 79Br in KBr, NaBr, and RbBr; 23Na in NaI, NaCl, and NaBr; 35Cl in NaCl and KCl; and 127I in NaI and KI. The obtained values of relaxation time T1 are an order of magnitude smaller than those calculated with the Debye-model phonon density of states and agree well with experiments. The temperature dependence of acoustic and optical phonon contributions to the nuclear relaxation rate (first-order Raman phonon process) are carried out in the temperature range 20 to 300 K for 23Na and 127I in NaI. The role of optical phonons becomes important from 77 K on; the temperature dependence of T1 agrees with experimental data throughout most of the temperature range studied (77–300 K), while differing quantitatively from the predictions obtained on the basis of the Debye model.

A nuclear magnetic resonance study of 1H, 23Na, and 31P relaxation and molecular dynamics in the sodium salts of some pyrophosphates

1989 ◽  
Vol 67 (6) ◽  
pp. 592-598 ◽  
Author(s):  
E. C. Reynhardt
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Laboratory Frame ◽  
Nuclear Magnetic Resonance Study ◽  
Spin Lattice Relaxation ◽  
Molecular Reorientation ◽  
Temperature Range ◽  
Spin Lattice ◽  
Second Moments ◽  
31P Relaxation

Proton second moments and spin-lattice relaxation times in the laboratory and rotating frames and 31P and 23Na spin-lattice relaxation times in the laboratory frame have been measured over the temperature region 295 > T > 100 K for the sodium pyrophosphate salts, Na2P2O7∙10H2O and Na2H2P2O7. Laboratory-frame 31P and 23Na spin-lattice relaxation times have also been measured over the same temperature range for Na4P2O7. In the case of Na4P2O7∙10H2O, the results show clearly that the H2O molecules execute a twofold jump motion at higher temperatures. The potential barriers to these motions range from 30 to 40 kJ/mol. The 31P and 23Na relaxations are also influenced by these motions. The [Formula: see text] ion in Na2H2P2O7 is stationary over the temperature range studied. T1(Na) is most probably dominated by acoustical lattice vibrations. The [Formula: see text] ion in Na4P2O7 is not involved in a molecular reorientation. A shallow T1(P) minimum of 55 s is associated with a limited motion of the pyrophosphate molecule.

Deuteron NMR of Methyl Groups in theTunneling Regime. A Single Crystal Study of Aspirin-CD3

1995 ◽  
Vol 50 (1) ◽  
pp. 95-116 ◽  
Author(s):  
A. Detken ◽  
P. Focke ◽  
U. Haeberlen ◽  
Z. Olejniczak ◽  
Z. T. Lalowicz ◽  
...  
Keyword(s):  
Single Crystal ◽  
Molecular System ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Temperature Limit ◽  
Spin Lattice Relaxation ◽  
Temperature Range ◽  
Spin Lattice ◽  
Potential Height ◽  
Deuteron Nmr

We report the first single crystal deuteron NMR spectra of CD3 groups which display the socalled ±ß, ±(|α| ± ß) and ±(2|α| ± ß) lines characteristic of rotational tunneling in a sufficiently clear manner to allow a quantitative comparison with the respective theory developed in 1988 by the group of W. Müller-Warmuth. The molecular system we study is aspirin-CD3. We recorded spectra for differently oriented single crystals and measured spin-lattice relaxation times T1 in a wide temperature range. At 12.5 K we exploit the dependence of the ±(|α| ± ß) and ±(2|α| ± ß) lines on the orientation of the applied field B0 for determining the equilibrium orientation of the CD3 group in the crystal lattice. The spectra display features which allow, by comparison with simulated spectra, a measurement of the tunnel frequency vt. Its low temperature limit is (2.7 ± 0.1) MHz. It allows to infer the height V3 of the potential V(φ) in which the CD3 group moves, provided that this potential is purely threefold. We get V3 = (47.2 ± 0.5) meV. The transition from the tunneling to the classical, fast reorienting regime occurs in the 15 K ≲ T ≲ 35 K temperature range. In this range we observe a broadening, merging and eventually narrowing of the ± |α| and ±2|α| lines in very much the way predicted by Heuer. His theory, however, must be extended by taking into account all librational levels. The behaviour of the ± ß lines in the transition temperature range signalizes a reduction of the observable tunnel frequency with increasing temperature. This reduction allows an independent measurement of the potential height and represents a test of the assumption of a purely threefold potential. From the T1 -data we derive the temperature dependence of the correlation time Ƭc of the reorientational jumps. The plot of log Ƭc vs. 1 /T follows a straight line for more than five decades. From its slope we get yet another independent number for the potential height. It agrees well with the other ones, which confirms the assumption of the essentially threefold potential V(φ) in aspirin-CD3.

Molecular Motions in Solid [Sb(CH3)4]PF6. A Combined 11H,9F Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Study

1992 ◽  
Vol 47 (5) ◽  
pp. 689-701 ◽  
Author(s):  
Günter Burbach ◽  
Norbert Weiden ◽  
Alarich Weiss
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Methyl Group ◽  
Temperature Range ◽  
Spin Lattice ◽  
Group Rotation ◽  
Methyl Group Rotation

Abstract The molecular dynamics of tetramethylstibonium hexafluorophosphate, [Sb(CH3)4]PF6, is investigated over a broad temperature range. NMR spin lattice relaxation times T1 and the NMR second moments of the 1H and 19F nuclei were determined in the range 8.6 ≦ T/K ≦ 332.3 for polycrystalline [Sb(CH3)4]PF6. The complex cation undergoes isotropic tumbling for T > 260 K and thermally activated methyl group rotation in the temperature range T < 196 K. The activation energies for the transition from methyl group rotation to cation reorientation, as derived from NMR wideline (18.1 kJ/mol) and relaxation (22.7 kJ/mol) measurements, match. At very low temperatures pseudo classical line narrowing is observed, indicating tunneling motions of the methyl groups. The existence of two crystallographically inequivalent methyl groups is found by X-ray structure analysis at room temperature. The space group is P63mc, Z = 2; a = 738.6 pm, c = 1089.3 pm. It is confirmed by two steps in the temperature dependence of the signal intensity of the quasielastic line in neutron fixed window measurements in the temperature range 2 < T/K <148. The low temperature spin lattice relaxation times can be explained qualitatively by contributions of two crystallographically inequivalent methyl groups. Apparent activation energies for the two crystallographically different methyl groups are estimated. The complex anion undergoes isotropic tumbling in the temperature range 95 < T/K < 330. Above 330 K additionally translational motion is activated. Below 95 K the rotational motion of PF-6 is freezing in via an uniaxial state in range 40 < T/K <80. Activation energies for both isotropical tumbling (10.5 kJ/mol) and uniaxial rotation (5.8 kJ/mol) have been derived from 19F NMR spin lattice relaxation

Proton and Fluorine-Spin-Lattice Relaxation in Poly crystalline FeSiF6 • 6 H2O

1981 ◽  
Vol 36 (6) ◽  
pp. 637-642 ◽  
Author(s):  
H. Rager
Keyword(s):  
Sharp Increase ◽  
Relaxation Times ◽  
Larmor Frequency ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Spin Lattice Relaxation ◽  
Temperature Range ◽  
Spin Lattice ◽  
Nuclear Spin Lattice Relaxation ◽  
Standard Pulse

Abstract The proton and fluorine nuclear spin-lattice relaxation has been measured in FeSiF6 • 6H2O in the temperature range 130 K ≦ T ≦ 420 K with standard pulse methods at 30 MHz. The relaxation times, T1(1H) and T1(19F), decrease with decreasing temperature according to the expression T1=a(I)exp(-Δ/T) (I = 1H, 19F). They show no significant dependence on the Larmor frequency. Thus, the unpaired Fe2+ electrons are mainly responsible for the proton and fluorine spin-lattice relaxation. The relaxation mechanism is described by an Orbach process. The ratio T1(19F)/T1(1H) is relatively constant over the whole temperature range investigated. This is explained by the strong H ... F bonds in FeSiF6 · 6H2O. The sharp increase of T1(1H) and T1(19F) at 224 K is attributed to the phase transition, which probably alters the crystal field at the Fe2+ centers

The effects of high temperatures (29–123 °C) on critical micelle concentrations in solutions of potassium n-octanoate in deuterium oxide: A nuclear magnetic resonance study

1986 ◽  
Vol 64 (9) ◽  
pp. 1823-1828 ◽  
Author(s):  
M. A. Desando ◽  
L. W. Reeves
Keyword(s):  
Chemical Shifts ◽  
Deuterium Oxide ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Nuclear Magnetic Resonance Study ◽  
Spin Lattice Relaxation ◽  
Spectral Parameters ◽  
Critical Micelle Concentrations ◽  
Temperature Range ◽  
Spin Lattice

Critical micelle concentrations have been determined for potassium n-octanoate in deuterium oxide over a wide temperature range, 29–123 °C, from the concentration dependence of proton nmr spectral parameters (peak positions, and vicinal splitting values of the α-CH2 multiplet) and carbon-13 nmr chemical shifts. The c.m.c. varies from ca. 0.30 m at ca. 30 °C to ca. 0.50 m at ca. 120 °C and is at a minimum (0.30–0.35 m) in the temperature range ca. 30–50 °C. 23Na+ spin-lattice relaxation times reveal that a co-counterion (Na+) different from that of the surfactant counterion (K+) reflects the micellization process. A second critical micelle concentration has been observed around 1.0 m at ca. 30 °C.

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