Nuclear magnetic relaxation in [sup 13]CH[sub 2] and [sup 13]CH[sub 3] coupled spin systems and variable angle spinning lineshape analysis for quadrupolar nuclei with half integer spins

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:6960435

Zheng, Z

The carbon-13 multiplet spin-lattice relaxation in [sup 13]CH[sub 2] and [sup 13]CH[sub 3] spin systems is studied in detail by various nonselective and selective pulse techniques. Simultaneous fitting of the resulting relaxation curves with various rates and initial conditions allows for the extraction of both auto- and cross-correlated dipolar spectral densities which can provide detailed information on the molecular anisotropic reorientation. In addition, the [sup 13]CH[sub 3] coupled spin relaxation can characterize the methyl internal rotation dynamics. The cross-correlation between the dipolar and chemical shift anisotropy (CSA) interactions is found to be appreciable. Dipolar-CSA cross-correlated spectral densities introduce relaxation pathways that couple together magnetization modes with different spin inversion symmetries. Consideration of the dipolar-CSA cross-correlated spectral densities not only improves the accuracy of the measurement of dipolar spectral densities but also allows for the determination of the dipolar-CSA cross-correlated spectral densities themselves, providing a new measure of the anisotropy of the shielding tensor. NMR spectroscopy of quadrupolar nuclei in solids generally yields broad lines even when magic angle spinning is applied. Broadening of the central transition of quadrupolar nuclei with half integer spins is caused by the anisotropy of the second order quadrupolar interaction. A straightforward approach is presented that combines average Hamiltonian theory and a numerical solution of a classical banded matrix describing the equation of motion for a quadrupolar nucleus under variable angle sample spinning conditions. At either of two fourth rank magic angles, a simple three parameter lineshape is obtained, and the three breakpoints are related directly to the quadrupolar constant and its asymmetry parameter.

• Research Organization: Utah State Univ., Logan, UT (United States)
• OSTI ID: 6960435
• Country of Publication: United States
• Language: English

Related Subjects

665100* -- Nuclear Techniques in Condensed Matter Physics -- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKYL RADICALS
CARBON 13
CARBON ISOTOPES
CLOSED CONFIGURATIONS
EVEN-ODD NUCLEI
ISOTOPES
LIGHT NUCLEI
MAGNETIC FIELD CONFIGURATIONS
METHYL RADICALS
METHYLENE RADICALS
MULTIPOLAR CONFIGURATIONS
NMR SPECTRA
NUCLEI
QUADRUPOLAR CONFIGURATIONS
RADICALS
RELAXATION
SOLIDS
SPECTRA
SPIN-LATTICE RELAXATION
STABLE ISOTOPES