Multinuclear Magnetic Resonance Study of Sodium Salts in Water Solutions

The small amounts of gaseous 3He dissolved in low concentrated water solutions of NaCl, NaNO3 and NaClO4 were prepared and examined by 3He-, 23Na-, 35Cl- and 15N-NMR spectroscopy. This experimental data, along with new theoretical shielding factors, was used to measure the 23Na nuclear magnetic moment against that of helium-3 μ(23Na) = +2.2174997(111) in nuclear magnetons. The standard relationship between NMR frequencies and nuclear magnetic moments of observed nuclei was used. The nuclear magnetic shielding factors of 23Na cation were verified against that of counter ions present in water solutions. Very good agreement between shielding constants σ(3He), σ(23Na+), σ(35Cl‒), σ(35ClO4‒), σ(15NO3‒) in water at infinite dilution and nuclear magnetic moments was observed for all magnetic nuclei. It can be used as a reference nucleus for calculating a few other magnetic moments of different nuclei by the NMR method. An analysis of new and former μ(23Na) experimental data obtained by the atomic beam magnetic resonance method (ABMR) and other NMR measurements shows good replicability of all specified results. The composition of sodium water complexes was discussed in terms of chemical equilibria and NMR shielding scale.

Stray-field imaging of quadrupolar nuclei of half integer spin in solids

A report is presented on the observation of Hahn echoes from the following quadrupolar nuclei of half integer spin (I) in polycrystalline solids in the large static magnetic field gradient (37.5 T/m) which exists in the fringe field of a superconducting solenoid: 7Li, 23Na, 11B, 65Cu (I = 3/2); 27Al (I = 5/2); 51V, 59Co (I = 7/2); and 115In (I = 9/2). 23Na echo-trains from NaCl (with non-selective excitation) and from Na2SO4 (with selective excitation) are compared quantitatively for two different RF pulse sequences: 90x-(tau-90y-tau-echo-)n and 90x-(tau-90x-tau-echo-)n. The signals obtained from RF pulses corresponding to non-selective 90 degrees pulses were shown to be quantitative, whereas in the selective case smaller signals were obtained since only the central transition contributed. The loss of signal from this cause can be distinguished from small signals resulting from low density of nuclei by use of the second sequence. A 7Li image obtained from LiF in a cylindrical glass-vial is shown.

Analytical treatment of the variable-angle sample spinning nuclear magnetic resonance spectra in the presence of the second-order quadrupole interaction. Determination of the quadrupole parameters and the chemical shift tensor

The analytical expressions for the transition probability of the central transition of the variable-angle sample spinning nuclear magnetic resonance (VAS NMR) spectrum for non-integral spins in the presence of second-order quadrupole interactions are derived on the basis of the stationary perturbation theory. The modulating parameters of the VAS NMR spectrum due to the time-dependent part of the quadrupole energy are found to be different (asymmetry parameter eta > 0.1) from those obtained from the average Hamiltonian theory. Using the conditions for saddle points and local maxima, it has been observed that there is a range of values for sample spinning angle beta around 32, 44 and 72 degrees to obtain the single peak; the range width can indicate the value of eta. Analytical expressions for the single-peak positions corresponding to beta around 32, 44 and 72 degrees are derived in terms of quadrupole parameters and chemical shift tensor. Further, we have described an analytical method to find the principal values of the chemical shift tensor in addition to the quadrupole parameters, using VAS NMR. As an illustration, the quadrupole parameters are computed for Na2MoO4 and Na2SO4 and compared with the values available in the literature (computed from wide-line NMR and magic-angle sample spinning (MAS) NMR data using the position of peaks and shoulders). For Na2MoO4 the principal values of the chemical shift tensor are found to be +17.5, -12 and -6.5 ppm. The present method is accurate and easy to apply as it involves only the positions of peaks and not of shoulders.(ABSTRACT TRUNCATED AT 250 WORDS)

Sideband analysis in DOR NMR spectra. II. Real finite inner-rotor speed

DOR (double orientation rotation) solid-state NMR technique is analyzed specifically in the case where numerous (> 4) sidebands are observed on the spectrum. In this case, a rough spectrum analysis leads to the false observation of several impurity species. The total "visible" intensity is smaller than the real one. This may lead to an apparent relative concentration change when several species with very different quadrupole interactions coexist in the sample. Contrary to the MAS technique, the correct analysis of DOR spectra with sidebands very often necessitates the simultaneous introduction of CSA and quadrupole interactions.

Sideband analysis in DOR NMR spectra. I. "Infinite" inner-rotor speed

DOR (double orientation rotation) solid-state NMR spectra are analyzed. All mathematical tools useful for describing the DOR spectra of nuclei simultaneously subjected to CSA and quadrupole interactions with non-coincident PAS are developed. The "infinite" inner-rotor speed approximation is described. The corresponding spectra observed in synchronized or unsynchronized experiments are analyzed. The rf pulse and recycle time effects are observed and explained. The comparison of MAS and DOR spectra on several compounds allows the determination of when the DOR technique is preferred to the MAS technique.