The temperature dependence of the 15N and 133Cs NMR spin-lattice relaxation times, the 15N spin-spin relaxation time, and the 15N and 133Cs spectra of CsNO2 was observed in the plastic phase (209.2 < T < 673 K (m. p.)) and the low-temperature phase (Phase II). In Phase II we found the NO-2 180°-flip, which could be attributed to the anomalous increase of the heat capacity curve, and determined the activation energy of this motion to be 8.7-11.7 kJ mol-1. The 15N and 133Cs spectra in this phase are inconsistent with the reported crystal structure R3̅m and can be explained by lower crystal symmetry. In the plastic phase we detected a new anionic motion with 11 kJ mol-1 , an isotropic NO-2 reorientation with 8.5-9 kJ mol-1, and ionic self-diffusion with 47 kJ mol-1. The presence of ionic self-diffusion was confirmed by measuring the electrical conductivity.
Abstract
Nuclear magnetic resonance measurements have been made on natural rubber to examine how frequency, temperature, and crystallinity affect the nuclear relaxation. Moecular motions were studied by observing NMR linewidths and spin-lattice relaxation times at temperatures between −100° and 100° C, and at radio frequencies between 2 and 60 Mc. The effect of crystallinity was seen in measurements on stark rubber. The relation between frequency and temperature in the spin-lattice relaxation process is examined in terms of the Arrhenius equation and the WLF expression. The importance of using frequency as a variable in NMR studies of molecular motion is stressed.
AbstractThe main goal of our novel NMR experiments on confined liquids was to determine the effects of pressure on the dynamics of liquids in the surface layer by using the twostate, fast exchange model and compare them to the pressure effects observed for bulk liquids. With this goal in mind, the deuteron NMR spin-lattice relaxation times, T1, in liquid pyridine-d5, nitrobenzene-d5, and methylcyclohexape-d confined to sol-gel porous silica glasses with pore radii in the range from 18Å to 49˚A were measured as a function of pressure up to 5 kbar at 300 K. In another set of high resolution natural abundance 13C NMR experiments, the 13C relaxation behavior of each carbon in 2- ethylhexyl benzoate model lubricant was measured as a function of pressure in porous silica glasses. In fact, the described experimental approach which allows investigation of the effects of pressure on the dynamic behavior of surface-layer liquids, may provide a new tool in studies of model liquid lubricants at extreme conditions of pressure and temperature. In addition selected results of a recent study of acetonitrile-d3 are reviewed. The 2H and 14N spin-lattice relaxation times of acetonitrile-d3 in porous silica glasses were measured in order to study the confinement effects on the anisotropic reorientation characterized by rotational diffusion constants, D⊥ and D‖, of this symmetric-top molecule.
Abstract The dynamics of water molecules intercalated in D2O saturated synthetic and natural smectites, and a synthetic Na-fluormica were studied by measurements of solid state 2H NMR spectra and spin-lattice relaxation times at 150 - 370 K. The obtained results could be explained by the 2-site flip, the C2 rotation and the isotropic rotation of the D2O molecules in smectites. In fluormica, the isotropic motion was undetectable, but the axial rotation of the hydration sphere as a whole was observed. The activation energies and correlation times of the C2 rotation were almost independent of the interlayer cations but depended on the character of clay-layers.
The order–disorder behaviour of 1-chloroadamantane (1-C10H15Cl) has been investigated by differential scanning calorimetry, and variable-temperature vibrational and 13C NMR spectroscopy. The factor group splittings in the vibrational spectra are in accord with the known crystal structures of the two phases. The 13C spin-lattice relaxation times and dipolar dephasing measurements have been analysed to give the barriers to rotation in both phases and to determine the nature of the rotations in each phase. In the ordered phase, the motion is limited to rotation about the molecular axis. In the disordered phase, additional motions occur about axes through the tertiary carbon atoms.
We carried out 125Te NMR studies of a WTe2 topological Weyl semimetal at temperatures of 41 and 293 K. Measurements were performed using a pulse Bruker Avance 500 NMR spectrometer. 125Te NMR spectra were obtained for the WTe2 single crystal at the orientation of the crystalline c axis parallel and perpendicular to the quantized field. We ascribed the complex spectra to four non-equivalent tellurium sites in the WTe2 crystalline structure. The recovery of the longitudinal magnetization was studied after the pulse saturation of particular lines in the spectra. We observed the single-exponential relaxation. The frequency shifts and widths of the spectral lines differed insignificantly at two temperatures while the spin-lattice relaxation times at 41 K were by a factor of approximately 30 greater than the relevant times at room temperature. Strong temperature dependence of relaxation was suggested to be due to the contribution of Weyl quasi-particles below the topological phase transition.
Abstract39K, 87, 85Rb, 133Cs, 205T1, and 1, 2H NMR spin-lattice relaxation times T1 and 14N NQR spin-lattice relaxation times T1Q were determined for R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4). T1 of 39K and 87Rb showed very short values in the incommensurate phase as compared with those in the other phases. When the commensurate-incommensurate phase transition point is approached from below, 14N T1Q of the R = K, Rb, Tl, and NH4 compounds showed rapid decrease. On the other hand, that of the R = Cs compound began to decrease first after passing beyond the corresponding transition point. The difference of the T1Q behavior may be ascribed to the difference of the condensed phonon mode in the incommensurate phase.
Mercury-199 spin-lattice relaxation times are reported for several mercury(II) compounds at 5.875 and 9.40 T. From the field dependence of T1, in Hg(CN)2, Hg(CH3)2, and Hg(C6H5)2, 199Hg chemical shielding anisotropies of 3800, 5820, and 5800 ppm are calculated. The errors in these of estimates of Δσ are at least 10%. Some implications of the large Δσ(199Hg) values in high field nmr studies are discussed.
15N and 133Cs Solid NMR Studies on Ionic Dynamics in Plastic CsNO2