Nuclear magnetic resonance studies of half-integer quadrupolar nuclei : sensitivity enhancements using double frequency sweeps

摘要

Exploiting adiabatic passages of the spin transitions, this thesis reports sensitivity enhancements of the MAS and MQMAS experiments on half-integer quadrupolar nuclei. The processes governing frequency sweeping are described. During such experiments the irradiation frequency sweeps through the different resonance frequencies of the spin system. Such passages can invert spin transitions if they are adiabatic. An analytical description of the adiabatic passages reveals that the efficiency of this process is measured by the adiabaticity parameter. A deep understanding of these phenomena allows one to manipulate population and coherences of the spin system in a profitable way that results in sensitivity enhancement of the MAS and MQMAS experiments. Having an increased sensitivity, these experiments are able to unravel structural information which were thus far inaccessible. This thesis successfully reports the first high-resolution Al MQMAS spectra of a Bronsted acidic sites in the H-ZSM5 zeolite