Spin–lattice relaxation and hydrodynamical rotation of triphenylene

1977 ◽  
Vol 55 (20) ◽  
pp. 3602-3608 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Brian A. Pettitt ◽  
Werner Danchura
Keyword(s):  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Hindered Rotation ◽  
Spin Lattice ◽  
Slip Boundary ◽  
The Times ◽  
Dynamic Rotation ◽  
C Nmr

The viscosity and temperature dependence of 1H, 2H, and 13C nmr relaxation rates of triphenylene were investigated. The observed η/T dependence of the reorientation correlation time, τc, is compared with that derived from the work of Hu and Zwanzig based on hydro–dynamic rotation with 'stick' and 'slip' boundary conditions. In the hydrodynamic regime,τ = Cη/T. The observed slope, Cexperimental, is 6.2 ± 2 ns K/cP and the calculated values are Cslip = 4.1 ± 0.6 ns K/cP and Cstick = 31.0 ± 3.1 ns K/cP. These data imply that the reorientation of triphenylene obeys a near-slip condition. That is, rotation in the plane of the molecule encounters little resistance, but rotation of the plane of the molecule is resisted by shear forces in the solvent displaced during rotation. Expressions are given for Boltzmann-averaged free rotation times and comparisons are made with the η = 0 intercept and the times for slightly hindered rotation.

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.

Ionic mobility in Nasicon-type LiMIV2(PO4)3 materials followed by 7Li NMR spectroscopy.

2011 ◽  
Vol 1313 ◽  
Author(s):  
K. Arbi ◽  
I. Sobrados ◽  
M. Hoelzel ◽  
A. Kuhn ◽  
F. Garcia-Alvarado ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Impedance Spectroscopy ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Ionic Mobility ◽  
Spin Lattice Relaxation ◽  
Pulse Field ◽  
Relaxation Rates ◽  
Arrhenius Behavior ◽  
Spin Lattice

AbstractLithium mobility in LiM2(PO4)3 compounds, with M= Ge, Ti, Sn, Zr and Hf, has been investigated by 7Li Nuclear Magnetic Resonance (NMR) spectroscopy in the temperature range 100-500 K. From the analysis of 7Li NMR quadrupole interactions (CQ and η parameters), Li sites occupancy and exchange processes between structural sites have been studied. Below 250K, Li ions are preferentially located at M1 sites in rhombohedral phases, but occupy M12 sites in triclinic ones. At increasing temperatures, Li mobility has been deduced from spin-spin () and spin-lattice relaxation () rates. In this analysis, the presence of two relaxation mechanisms in plots has been associated with departures of conductivity from the Arrhenius behavior. At high temperatures, residence times at M12−T11−T11−T1 and M12 sites become similar and conductivity significantly increase. This superionic state can be achieved by enlarged order-disorder transformations in rhombohedral phases, or by sharp first order transitions in triclinic ones. Results described in the LiTi2(PO4)3 sample have been compared with those obtained in rhombohedral Li1+xTi2-xAlx(PO4)3 and LiTi2-xZrx(PO4)3 series showing respectively higher and lower conductivities. In the case of Li1.2Ti1.8Al0.2(PO4)3, displaying the highest reported conductivity, NMR results are discussed in relation with those obtained by Neutron Diffraction (ND) and Impedance Spectroscopy (IS). Diffusion coefficients determined by NMR Pulse Field Gradient (PFG) technique are similar to those deduced from Impedance Spectroscopy and NMR relaxation data.

Boron-11, boron-10, and nitrogen-14 NMR relaxation rates and quadrupole coupling constants in BH3NH3

1992 ◽  
Vol 70 (9) ◽  
pp. 2420-2423 ◽  
Author(s):  
Glenn H. Penner ◽  
Stephen I. Daleman ◽  
Angela R. Custodio
Keyword(s):  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Orbital Theory ◽  
Spin Lattice ◽  
Quadrupolar Coupling ◽  
Field Gradients

The 11B, 10B, and 14N spin–lattice relaxation times (T1) for aqueous solutions of BH3NH3 were measured by NMR spectroscopy. The results of this investigation are consistent with the nuclear quadrupolar coupling constants reported in previous nuclear quadrupolar resonance and microwave studies. The activation energy associated with rotational reorientation of BH3NH3 in aqueous solution is 11.7 ± 0.6 kJ/mol. Electric field gradients were calculated at various levels of abinitio molecular orbital theory, in order to obtain theoretical 14N and 11B quadrupolar coupling constants. At the highest level of calculation (CI(SD)/6-31G**//MP2/6-31G**), these are in agreement with recently reported microwave results but not with previously reported NQR experiments.

89Y AND 63Cu NMR-NQR AND SUSCEPTIBILITY STUDY OF UNDERDOPED SUPERCONDUCTING Y1-xCaxBa2Cu3O6.1

2000 ◽  
Vol 14 (25n27) ◽  
pp. 2797-2802 ◽  
Author(s):  
A. CAMPANA ◽  
P. CARRETTA ◽  
M. CORTI ◽  
A. LASCIALFARI ◽  
A. RIGAMONTI ◽  
...  
Keyword(s):  
Magnetic Moments ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Superconducting Phase ◽  
Spin Fluctuations ◽  
Spin Lattice Relaxation ◽  
Freezing Process ◽  
Relaxation Rates ◽  
Spin Lattice ◽  
Spin Freezing

89 Y NMR relaxation has been used to study the spin freezing process in Y 1-x Ca x Ba 2 Cu 3 O 6.1. Substituting Ca 2+ for Y 3+ in the parent antiferromagnetic YBa 2 Cu 3 O 6.1 leads the system in the underdoped superconducting phase. In the normal state of the sample at x=0.15 the spin-lattice relaxation rate, which is not affected by the antiferromagnetic correlation of the Cu 2+ magnetic moments, still evidences a decrease of (1/ T 1 T ) on cooling, indicative of a pseudo-gap opening in the density of states around the Fermi energy. The most relevant result is found in the superconducting phase, where the recovery of the 89 Y NMR signal displays two distinct laws, pointing out different relaxation mechanisms without common spin temperature. One exponential recovery law yields a decay rate which decreases on cooling, as expected in the superconducting phase. The second relaxation process turns out to be described by a stretched exponential, with fast relaxation rates, strongly increasing on cooling, with a characteristic spin fluctuations frequency reaching the 20 MHz range at about 8 K. This observation is interpreted as the direct experimental evidence of the coexistence, at mesoscopic level, of superconductive and spin-glass like phases, the spin freezing process being described by the fast rate of the nuclear relaxation.

Analysis of Spin Polarisation Transients in Periodically Photo-excited Triplet States

1975 ◽  
Vol 30 (5) ◽  
pp. 571-582 ◽  
Author(s):  
C. J. Winscom
Keyword(s):  
Lattice Relaxation ◽  
Rectangular Pulse ◽  
Decay Rates ◽  
Spin Lattice Relaxation ◽  
Pulse Excitation ◽  
Triplet States ◽  
Relaxation Rates ◽  
Spin Sublevel ◽  
Spin Lattice ◽  
The Individual

Abstract The behaviour of spin sublevel populations with time following periodic photo-excitation is ex-amined. The treatment is limited to conditions of magnetic field strength and temperature for which the spin lattice relaxation rates dominate the individual spin sublevel decay rates. The response of the system to three modes of excitation is considered: (i) continuous excitation using a time-independent intensity (ii) periodic rectangular pulse excitation and (iii) periodic waveform excitation. A convenient correspondence between the various forms of solutions is pointed out. The requirements of an experiment to determine spin-lattice relaxation rates in organic triplets at 77 K are discussed.

Anion reorientations and cation diffusion in a carbon-substituted sodium nido-borate Na-7,9-C2B9H12: 1H and 23Na NMR studies

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Alexander V. Skripov ◽  
Olga A. Babanova ◽  
Roman V. Skoryunov ◽  
Alexei V. Soloninin ◽  
Terrence J. Udovic
Keyword(s):  
Lattice Relaxation ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Cation Diffusion ◽  
Relaxation Data ◽  
Nmr Studies ◽  
Spin Lattice ◽  
Jump Rate ◽  
Disordered Phase

Abstract Polyhydroborate-based salts of lithium and sodium have attracted much recent interest as promising solid-state electrolytes for energy-related applications. A member of this family, sodium dicarba-nido-undecahydroborate Na-7,9-C2B9H12 exhibits superionic conductivity above its order-disorder phase transition temperature, ∼360 K. To investigate the dynamics of the anions and cations in this compound at the microscopic level, we have measured the 1H and 23Na nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates over the temperature range of 148–384 K. It has been found that the transition from the low-T ordered to the high-T disordered phase is accompanied by an abrupt, several-orders-of-magnitude acceleration of both the reorientational jump rate of the complex anions and the diffusive jump rate of Na+ cations. These results support the idea that reorientations of large [C2B9H12]− anions can facilitate cation diffusion and, thus, the ionic conductivity. The apparent activation energies for anion reorientations obtained from the 1H spin-lattice relaxation data are 314 meV for the ordered phase and 272 meV for the disordered phase. The activation energies for Na+ diffusive jumps derived from the 23Na spin-lattice relaxation data are 350 and 268 meV for the ordered and disordered phases, respectively.

An experimental evaluation of simplified procedures for determining the proton spin–lattice relaxation rates of natural products

1980 ◽  
Vol 58 (19) ◽  
pp. 2016-2023 ◽  
Author(s):  
Lawrence D. Colebrook ◽  
Laurance D. Hall
Keyword(s):  
Natural Products ◽  
Lattice Relaxation ◽  
Null Point ◽  
Proton Spin ◽  
Computational Method ◽  
Spin Lattice Relaxation ◽  
Relaxation Rates ◽  
Spin Lattice ◽  
Simplified Procedures

A general discussion is given of the determination of the proton spin–lattice relaxation rates of natural products, with particular emphasis on use of the null-point method which, for the systems studied here, gives identical results with those obtained via the conventional (and relatively time consuming) computational method.

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