Search

A quadrupole echo method for searching for the nuclear hexadecapole interaction (HDI) is described. A sequence of three radio frequency pulses applied at times 0, τ, and nτ (n>1) gives a simple pattern of nuclear spin (5)/(2) echoes when only the nuclear Zeeman and quadrupole interactions are present. Calculations for n=2.5, 3.0, 4.0, and 5.0 show that these patterns undergo an elaborate change when the HDI is also present and that these echo patterns are unique to the HDI. Three pulse echoes were used to search for the 127I HDI in a single crystal of KI but, for this sample, a two pulse sequence was found to be more effective. For KI, 2.8 kHz is the estimated magnitude of the 127I hexadecapole coupling constant, eHV(4)/h, where eH is the 127I electric hexadecapole moment and V(4) is a fourth derivative of the electrostatic potential at the nuclear site. This is the smallest HDI measured in a solid so far. [ABSTRACT FROM AUTHOR]

Using multipulse techniques, principal values of the proton nuclear magnetic resonance (NMR) chemical shift tensors were measured at room temperature for the monoclinic form of oxalic acid, potassium hydrogen oxalate, and potassium hydroxide. The isotropic and perpendicular shifts of the first two compounds, which are of medium hydrogen bond strength, were found to fit the linear correlation with O···O distance, RO·O, established by Rohlfing, Allen, and Ditchfield for medium and strongly O–H···O hydrogen bonded solids. Although KOH is very weakly hydrogen bonded, the shifts were also found to conform to the correlation, at least as well as does the other data, thus extending this to weakly hydrogen bonded solids. An empirical correlation of the isotropic and perpendicular shifts with exp(-RO·O/ρ), where RO·O is in Å and ρ is 0.94 Å, is given here which has better agreement with the data and has an interpretation in terms of a simple ionic model of an O–H···O bond. [ABSTRACT FROM AUTHOR]

The proton NMR shielding tensor was measured at room temperature in the hexagonal layered compound magnesium hydroxide. The isotropic shielding is 29.9±2 and the anisotropy is 12.7±2 ppm, on the 1H absolute scale. From a Gierke and Flygare (GF) analysis of the data the OH- spin–rotation constant was found to be 51±14 kHz. The GF contributions from the neighbors of a given OH- group were subtracted from the experimental shielding and corrections were made for the effects of vibrational motion to give an isotropic shielding of 29.9±2, with an anisotropy of 13.7±2 ppm, for an isolated OH-. The OH- shielding anisotropy is in good agreement with the ab initio calculations of Ratcliffe et al., but the isotropic shielding is not. Proton spin–lattice relaxation measurements at 300 and 77 K gave evidence of proton conductivity in Mg(OH)2. [ABSTRACT FROM AUTHOR]

A 19F NMR multipulse measurement of the chemical shift in a single crystal of cubic RbCaF3 gave -47.0±3 ppm as the isotropic value with respect to C6F6, and 128.7±6 ppm as the anisotropy. The shielding is accounted for by the usual diamagnetic and paramagnetic ionic overlap and covalent terms. As a result, the Ca++ -F- bond is estimated to be 98% ionic. No significant spectral changes were found when the crystal was cooled below the cubic to tetragonal phase transition temperature. Reasons for this are given. [ABSTRACT FROM AUTHOR]

Using NMR multipulse methods an upper limit of 20 kHz was established for the 115In hexadecapole coupling constant in InP. From the orientation dependence of the 31P second moment the magnitude of the 31P–115In exchange coupling constant and the pseudodipolar coupling constant were obtained. The results are 0.17±0.04 kHz, and -0.30±0.07 or -0.99±0.07 kHz, respectively. [ABSTRACT FROM AUTHOR]

Presents a study that performed proton shielding of the oxonium ion in perchloric acid monohydrate. Measurement of proton nuclear magnetic resonance hydrogen-oxygen principal axis shielding tensor values; Comparison of the proton shielding in hydrogen-oxygen and chlorine-oxygen compounds; Temperature by which the compounds were shielded.

Focuses on a study which examined the fluorine isotope shielding anisotropy in isostructural compounds. Information on the undoped single crystal used in the study; Multipulse absorption spectrum of the inorganic compound; Anisotropic chemical shifts of some fluoroperovskites.