Hydrosulfide-ion dynamics in cesium and rubidium hydrosulfide: a deuteron nuclear magnetic resonance study

1986 ◽  
Vol 64 (7) ◽  
pp. 833-838
Author(s):  
Kenneth R. Jeffrey ◽  
Roderick E. Wasylishen
Keyword(s):  
Quadrupole Interaction ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Site Symmetry ◽  
Time Data ◽  
Molecular Reorientation ◽  
Temperature Range ◽  
Spin Lattice ◽  
Nuclear Quadrupole

RbSD and CsSD have a multiplicity of solid-state phase transitions involving changes in the degree of order of the SD− ion. Because the deuteron has a nuclear quadrupole moment, the observed NMR spectrum reflects any changes that take place in the deuteron-site symmetry as a result of a phase change. Furthermore, the magnitude of the observed nuclear quadrupole interaction depends on the time average of the electric-field gradient at the deuteron site; this, in general, is a function of any molecular motion in the crystal. The nuclear spin–lattice relaxation times provide information about the time scale of any molecular reorientation taking place in the crystal structure. Deuteron NMR spectra and relaxation times are presented for RbSD and CsSD over the temperature range from 100 to 400 K. The spin–lattice relaxation time data show that there is reorientation of the SD− ion in the tetragonal phase of CsSD and in the trigonal phase of RbSD. While the correlation time for the reorientation changes from being short compared with the reciprocal of the quadrupole interaction to being the same order of magnitude in the temperature range studied, the deuterium NMR line shapes do not change substantially. It is concluded that the observed reorientation of the SD− ion in both RbSD and CsSD in the low-temperature noncubic phases is end-for-end flipping of the SD− ion since only reorientation by 180° leaves the static quadrupole splitting unchanged.

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.

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.

Molecular Reorientation in the Plastic Crystalline Phase of Tris

1979 ◽  
Vol 32 (4) ◽  
pp. 905 ◽  
Author(s):  
RE Wasylishen ◽  
PF Barron ◽  
DM Doddrell
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Molecular Reorientation ◽  
Liquid Phase Transition ◽  
X Ray ◽  
Spin Lattice

Carbon-13 N.M.R. spectra of tris(hydroxymethyl)aminomethane (Tris) have been measured between 407 and 461 K. Proton-decoupled 13C N.M.R. spectra of solid Tris between 407 K and its melting point are relatively sharp (v� < 30 Hz) indicating rapid overall molecular reorientation in this temperature range. It was not possible to detect a 13C N.M.R, signal for Tris below 407 K. The observed 13C N.M.R. spin-lattice relaxation times appear continuous across the solid ↔ liquid phase transition. From the temperature dependence of T1, a rotational activation energy of 51.6 � 6 kJ mol-1 is calculated, which indicates that the molecules must expend considerable energy in reorienting. The N.M.R. results are discussed in relation to previous differential scanning calorimetry and X-ray diffraction data which indicate that Tris undergoes a solid ↔ solid transition at 407 K.

Temperature Dependences of NQR Frequencies and Nuclear Quadrupole Relaxation Times of Chlorine in 2,6-Lutidinium Hexachlorotellurate (IV) as Studied by Pulsed NQR Techniques

1990 ◽  
Vol 45 (3-4) ◽  
pp. 485-489
Author(s):  
Keizo Horiuchi ◽  
Takashige Shimizu ◽  
Hitomi Iwafune ◽  
Tetsuo Asaji ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Quadrupole Relaxation ◽  
Spin Lattice ◽  
Resonance Frequencies ◽  
Temperature Dependences ◽  
Nuclear Quadrupole

Abstract The temperature dependences of the 35Cl NQR frequencies vQ and the nuclear quadrupole spin-lattice relaxation times T1Q in 2,6-lutidinium hexachlorotellurate (IV) was observed at various temperatures between 80 and 343 K. This crystal undergoes a phase transition at Tc = 229 K. A single and three pairs of 35Cl NQR frequencies were observed above and below Tc , respectively. The hysteresis of the phase transition and a discontinuity in the temperature dependence of the resonance frequencies at Tc indicate that this phase transition is of first order. Although the resonance frequencies of the pairs in the low temperature phase are very close to one another, T1Q and below Tc could be accurately determined by measuring the Fourier transform spectra of each line. Above ca. 250 K, T1Q showed an exponential decrease which is attributable to the overall reorientational motion of [TeCl6]2- with an activation energy of 82 kJ mol-1

A Nuclear Spin Relaxation Study of the Spin–Rotation Interaction in Symmetric Top Molecules

1972 ◽  
Vol 50 (12) ◽  
pp. 1262-1272 ◽  
Author(s):  
Robin L. Armstrong ◽  
James A. Courtney
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Spin Rotation ◽  
Spin Lattice Relaxation ◽  
Molecular Reorientation ◽  
Effective Spin ◽  
Spin Lattice ◽  
Simple Exponential Function ◽  
Symmetric Top Molecules

The spin–lattice relaxation times T1 of 1H, 19F, and 31P nuclei were measured in gaseous samples of BF3, CHF3, CH3F, PH3, and NH3 at room temperature for densities from 0.03 to 10 amagat. In several cases the behavior of T1 at the lowest densities snowed deviations from the linear variation characteristic of the extreme narrowing region. The spin–rotation interaction provides the dominant relaxation mechanism in all cases. The data are analyzed on the basis of the assumption that the collision modulated spin–rotation interaction may be described by a single correlation function which is a simple exponential function of time. Values of an effective spin–rotation constant and a cross section for molecular reorientation are obtained for each gas. The results obtained are compared with those available from other types of experiments. This comparison indicates that the theory for spin–lattice relaxation in dilute gases of symmetric top molecules needs to be carefully reassessed.

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

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