Molecular motion and barriers in N2H5Cl and N2H5Br studied by inelastic neutron scattering and proton magnetic resonance spin lattice relaxation

1978 ◽  
Vol 74 ◽  
pp. 1417 ◽  
Author(s):  
Christopher I. Ratcliffe ◽  
Basil A. Dunell ◽  
Thomas C. Waddington
Keyword(s):  
Magnetic Resonance ◽  
Neutron Scattering ◽  
Proton Magnetic Resonance ◽  
Molecular Motion ◽  
Inelastic Neutron Scattering ◽  
Lattice Relaxation ◽  
Inelastic Neutron ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Resonance Spin

A proton magnetic resonance relaxation study of molecular motions in trimethylamine-borane

1976 ◽  
Vol 54 (7) ◽  
pp. 1087-1091 ◽  
Author(s):  
T. T. Ang ◽  
B. A. Dunell
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Solid Phase ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Free Induction ◽  
Resonance Spin ◽  
Resonance Relaxation

Proton magnetic resonance spin–lattice relaxation times T1 have been measured for trimethylamine-borane from 120 to 380 K, a few degrees above the melting point. Minima in T1 at 157 and 259 K are attributed to threefold reorientation of each of the three methyl groups and the borane group and to threefold reorientation of the whole molecule about the B—N axis, respectively. Activation energies for these processes were found to be 3.3 and 6.7 kcal/mol. Abrupt changes in T1 at 350 and 360 K correspond exactly with heat capacity transitions observed by other workers. The time constant for the decay of the free induction signal (FID curve) changes by two orders of magnitude at 360 K. Having a value of some 3 ms above 360 K, it shows that there must be rapid diffusion as well as molecular tumbling in the highest temperature solid phase.

Rotational Excitations and Tunneling of Nonequivalent Methyl Groups in Tetramethylstibonium Iodide as Studied by Nuclear Magnetic Resonance and Inelastic Neutron Scattering

1991 ◽  
Vol 46 (9) ◽  
pp. 759-769 ◽  
Author(s):  
Günter Burbach ◽  
Alarich Weiss
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperatures ◽  
Inelastic Neutron Scattering ◽  
Lattice Relaxation ◽  
Inelastic Neutron ◽  
Spin Lattice Relaxation ◽  
Methyl Groups ◽  
Methyl Group ◽  
Spin Lattice

Abstract Nuclear magnetic resonance (NMR) and inelastic neutron scattering techniques (INS) have been applied to study the rotational motions and methyl group tunneling in tetramethylstibonium iodide, [Sb(CH3)4 ] I, over er a wide temperature range. Parameters describing the [Sb(CH3)4]+ cation tumbling and the methyl group reorientation at high temperatures and quantum mechanical tunneling of the methyl groups at low temperatures were determined. The results for INS and NMR experiments at low temperatures can be explained in terms of two crystallographically inequivalent methyl groups CH3(1) and CH3(2), which were established earlier by the crystal structure determination. In the INS spectra two tunneling lines at 22.0 μeV for CH3(1) and 1.05 μeV for CH3(2) with inelastic intensities in the ratio 3:1 were observed at T = 4 K. The activation energies derived from proton NMR spin-lattice relaxation time measurements for the thermally activated methyl group rotation are 1.50 kJ/mol for CH3(1) and 3.81 kJ/mol for CH3(2). They are in accordance with the activation energies obtained from neutron fixed-window measurements. The activation energy for [Sb(CH3)4]+ cation tumbling is 50.9 kJ/mol as determined from the high temperature spin-lattice relaxation behaviour. Rotational potentials for the methyl groups are derived. For both kinds of inequivalent methyl groups the threefold potential terms dominate; three- and sixfold potential contributions are shifted by 180°

Proton Magnetic Resonance Study of Molecular Motion in Solid Silver Sulfate Tetrammine, Ag2SO4 · 4NH3

1979 ◽  
Vol 34 (3) ◽  
pp. 333-339 ◽  
Author(s):  
Norbert Kummer ◽  
John L. Ragle ◽  
Norbert Weiden ◽  
Alarich Weiss
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Nmr Studies ◽  
Spin Lattice ◽  
Silver Sulfate ◽  
Proton Magnetic Resonance Study

Abstract The spin lattice relaxation time T1 and the second moment of the proton magnetic resonance were studied on polycrystalline samples of Ag2SO4 · 4NH3. The wideline NMR measurements show a rapid reorientation of the NH3 groups around their threefold axes in the temperature range 250 K ≦ T ≦ 380 K. Below T ≈ 250 K, the rotation of the NH3 starts freezing-in. From Ti measurements an activation energy of 27.5 kJ mol -1 for the rotation was found for temperatures above 210 K. Around 330 K a phase transition has been observed by T1 measurements which is not recognized by wideline NMR measurements in the range 77 K ≦ T ≦ 375 K. The results are discussed and compared with other NMR studies on solids containing NH3 groups.

A nuclear magnetic resonance investigation of n -pentane, n -hexane and cyclo pentane

1954 ◽  
Vol 222 (1151) ◽  
pp. 526-541 ◽  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Motion ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Kcal Mole ◽  
Second Moment ◽  
Spin Lattice ◽  
Second Moments

The nuclear magnetic resonance spectra and spin-lattice relaxation times have been measured for the protons in n -pentane (C 5 H 12 ), n -hexane (C 6 H 14 ) and cyclo pentane (C 5 H 10 ) all in the solid state. The temperature range covered was from 70° K to the melting-points of 143·4° K for n -pentane, 177·8° K for n -hexane and 179·4° K for cyclo pentane. In the case of n -pentane and n -hexane the second moments of the absorption lines were found to be smaller than the computed rigid lattice values over the. whole temperature range. Possible molecular motions which might cause this reduction are discussed. It is suggested that the most probable type of motion is reorientation of the methyl groups at the ends of each molecule about the adjacent C—C bonds. An analysis of the spin-lattice relaxation times shows that this reorientation process is governed by an activation energy of 2·7 kcal/mole for n -pentane and 2·9 kcal/mole for n -hexane, values which support the mechanism postulated. At the lowest temperature the absorption lines had not reached their full widths, even though the reorientation frequencies at these temperatures were considerably less than the line-widths. The experimental second moment for cyclo pentane below about 120° K indicates that the lattice is effectively rigid in this temperature region. The uncertainties in both the experimental and theoretical second moments do not allow a distinction to be drawn between the plane and puckered molecular models. At the temperature of the first transition (122·4° K) the line-width second moment and relaxation time all show a sudden decrease. The low value of second moment at the higher temperatures indicates that considerable molecular motion is occurring, the molecules rotating with spherical symmetry. The change in crystal structure at the temperature of the second transition (138·1° K) is thought to be a direct result of this spherical symmetry. As the temperature increases, the results indicate that more molecular motion must be occurring, and it is thought that the rotating molecules are diffusing through the lattice.

Polymer Relaxational Dynamics Associated With Ionic Conduction in Confined Geometry

2002 ◽  
Vol 756 ◽  
Author(s):  
J.-M. Zanotti ◽  
L. J. Smith ◽  
E. Giannelis ◽  
P. Levitz ◽  
D. L. Price ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Ionic Conduction ◽  
Inelastic Neutron Scattering ◽  
Mean Square Displacement ◽  
Lattice Relaxation ◽  
Inelastic Neutron ◽  
Spin Lattice Relaxation ◽  
Scattering Data ◽  
Melting Transition ◽  
Time Data

ABSTRACTResults of a quasi-elastic incoherent neutron scattering study of the influence of confinement on polyethylene oxide (PEO) and (PEO)8Li+[(CF3SO2)2N]- (or (POE)8LiTFSI) dynamics are presented. The confining media is Vycor, a silica based hydrophilic porous glass. We observe a strong slowing down of the bulk polymer dynamics under presence of Li salt. The confinement also affects dramatically the apparent mean-square displacement of the polymer. As supported by DSC measurements, the PEO melting transition at 335 K is strongly attenuated under confinement, suggesting that confinement modifies the global structure of the system, increasing the fraction of amorphous PEO by respect to crystalline phase. Local relaxational PEO dynamics is successfully described by the DLM (Dejean-Laupretre-Monnerie) model usually used to interpret NMR spin-lattice relaxation time data. The scattering vector dependence of the correlation times deduced from inelastic neutron scattering data is found to obey a power-law dependence. DSC and preliminary ionic conduction measurements are also presented.

scholarly journals Methyl Group Rotation and Tunnellingin Crystals of 5-Membered Ring Molecules

1988 ◽  
Vol 43 (1) ◽  
pp. 35-42 ◽  
Author(s):  
A.-S. Montjoie ◽  
W. Müller-Warmuth ◽  
Hildegard Stiller ◽  
J. Stanislawski
Keyword(s):  
Elevated Temperatures ◽  
Inelastic Neutron Scattering ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Inelastic Neutron ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Quantum Tunnelling ◽  
Spin Lattice

Abstract1H NMR spin-lattice relaxation times T1 and -if accessible -level-crossing peaks and inelastic neutron scattering spectra have been measured for solid 2-and 3-methylfuran, 2-and 3-methylthiophene, 3-and 4-methylpyrazole, 1-methylimidazole, and 5-methylisoxazole. From the tunnel splittings, the torsional excitations and the NMR relaxation rates, the molecular dynamics of the methyl rotators has been evaluated between the limits of quantum tunnelling at low temperatures and thermally activated random reorientation at elevated temperatures.

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