W. K. Rhim

Analysis of multiple pulse NMR in solids. II

A systematic method, an extension of the average Hamiltonian formalism, is presented for calculating the effects of pulse errors and imperfections in the multiple pulse nuclear magnetic resonance experiments. Application of this method to account for effects of pulse nonidealities such as phase errors, phase transient effects, pulse size errors, and rf inhomogeneity is found to agree with experimental observation, and the results furnish a basis for understanding the complex couplings between the pulse errors and other interactions such as the dipolar and the chemical shift Hamiltonians.

Development of an electrostatic positioner for space material processing

This paper describes an electrostatic positioning instrument which was developed at the Jet Propulsion Laboratory to enable experimenters to conduct containerless material science experiments in space. Samples that are to be studied are electrically charged and controlled by the electrostatic force produced by a set of properly arranged electrodes. Three different types of positioners are described, i.e., the dish type, the ring type, and the tetrahedral type. In all these systems, the positioning and the damping of the sample is accomplished by a feedback control system. The advantage of this electrostatic positioning method, in comparison to the other methods, such as acoustic and electromagnetic, lies in the fact that it can operate in a high vacuum and does not require the material to be electrically conductive as long as the material can carry a certain amount of charge.

19F Chemical Shift Tensor in Group II Difluorides

The multiple pulse nuclear magnetic resonance techniques have been used to measure the 19F chemical shift, or nuclear magnetic shielding, tensor in a series of Group II difluorides. For the cubic difluorides measured values relative to a C6F6 reference are: CaF2, −61 ppm; SrF2, −82; BaF2, −154 ppm; CdF2, +33 ppm; and HgF2, +32 ppm. For the two noncubic difluorides principal values of the chemical shift tensors relative to C6F6 are; for MgF2, +13, +28, and +43 ppm; and for ZnF2, +15, +38, and +59 ppm. The chemical shifts from the cubic difluorides were found to correlate well with electronegativities and a covalency parameter calculated from electron spin resonance superhyperfine interaction parameters. A theoretical calculation of the chemical shift tensor for MgF2 is presented and give good agreement with the experimental data, accounting for 90% of the chemical shift anisotropy.

Proton anisotropic chemical shift spectra in a single crystal of hexagonal ice

The proton anisotropic chemical shift spectra in a single crystal of hexagonal ice are reported for the first time. (AIP)

A multiple pulse zero crossing NMR technique, and its application to 19F chemical shift measurements in solids

A simple, multiple pulse ’’zero crossing technique’’ for accurately determining the first moment of a solid state NMR spectrum is introduced. This technique was applied to obtain the 19F chemical shift versus pressure curves up to 5 kbar for single crystals of CaF2 (0.29±0.02 ppm/kbar) and BaF2 (0.62±0.05 ppm/kbar). Results at ambient temperature and pressure are also reported for a number of other fluorine compounds. Because of its high data rate, this technique is potentially several orders of magnitude more sensitive than similar cw methods.

Calculation of spin–lattice relaxation during pulsed spin locking in solids

The spin–lattice relaxation time has been calculated for dipolar solids when the spins are locked by an rf pulse sequence with pulses of arbitrary angle and finite width. Expressions are given for the homonuclear case in general and for the heteronuclear case in the δ‐function limit. The results for the homonuclear case are experimentally confirmed using solid C6F12. The analysis shows that for small pulse angles, at which the direct spin heating effect is known to be small, the relaxation behavior will be identical to the cw irradiation case.

Highly flexible pulse programmer for NMR applications

A pulse generator for NMR application is described. Eighteen output channels are provided to allow use in both single and double resonance experiments. Complex pulse sequences may be generated by loading instructions into a 256‐word by 16‐bit program memory. Features of the pulse generator include programmable time delays from 0.5 μs to 1000 s, branching and looping instructions, and the ability to be loaded and operated either manually or from a PDP‐11/10 computer.

Heteronuclear spin dynamics using multiple pulse NMR techniques

Abstract : This manuscript briefly describes and demonstrates new and unique methods for controlling nuclear spin dynamics. Their largest impact is likely to be in furnishing means for obtaining structural information (precise bond angles and distances) which will be applicable to such systems as absorbed hydrocarbons. (Author)

Extraction of quadrature phase information from multiple pulse NMR signals

A multiple pulse sequence (8‐pulse sequence) used for high‐resolution solid state NMR is analyzed with regard to the information available from each of the four wide sampling windows. It is demonstrated that full quadrature phase information can be obtained using only a single phase detector and that, for the commonly encountered situation where the spectral width is much less than the folding frequency, the signals from the various windows can be combined easily using standard complex Fourier transform software. An improvement in the signal‐to‐noise ratio of √3 is obtained over either standard single of quadrature phase detection schemes. Procedures for correcting spectral distortions are presented.

NMR studies of electronic structure in crystalline and amorphous Zr2PdHx

Abstract The proton Knight shifts and spin-lattice relaxation times have been measured in crystalline and amorphous Zr 2 PdH x . Core-polarization from the Zr d-band dominates the proton hyperfine interactions. The density of Fermi level d-electron states is reduced in the amorphous phase relative to the electron density in crystalline Zr 2 PdH x .