Isotropic chemical shifts and quadrupolar parameters of oxygen-17 using dynamic-angle spinning NMR
- Lawrence Berkeley Laboratory, CA (United States)
Several oxygen-17-enriched silicates were studied using dynamic-angle spinning (DAS) NMR spectroscopy at two magnetic field strengths. The DAS method averages second-order quadrupolar interactions by reorienting a sample about a time-dependent axis, thereby yielding high-resolution spectra for half-odd integer spin quadrupolar nuclei such as oxygen-17. A narrow spectral line is observed for each distinct oxygen site in a powdered sample at the sum of the isotropic chemical shift and the field-dependent isotropic second-order quadrupolar shift. Using equations for the total shift observed at two field strengths, the chemical shift is uniquely determined together with a product of the quadrupolar coupling constant (C{sub Q} = e{sup 2}qQ/h) and the quadrupolar asymmetry parameter ({eta}). For one silicate, the authors demonstrate a computer program that uses the isotropic shifts and quadrupolar products as constraints and provides simulations of overlapped magic-angle spinning line shapes. In this way the quadrupolar parameters, C{sub Q} and {eta}, are determined separately for each crystallographic site. The silicates studied include the discrete orthosilicates larnite (Ca{sub 2}SiO{sub 4}) and forsterite (Mg{sub 2}SiO{sub 4}), as well as diopside (CaMgSi{sub 2}O{sub 6}), wollastonite (CaSiO{sub 3}), and clinoenstatite (MgSiO{sub 3}), which are minerals composed of chains of silicon-oxygen tetrahedra. 49 refs., 2 figs., 2 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 281154
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 17 Vol. 96; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
Similar Records
Solid-state oxygen-17 nuclear magnetic resonance spectroscopic studies of alkaline earth metasilicates
Solubility relationships of calcium and magnesium minerals in processed oil shales