Phase cycling methods and spinning sideband manipulation in solid-state NMR

Abstract

In solid-state nuclear magnetic resonance, phase cycling is used to compensate for experimental imperfections and to cancel out undesired signal components. This is achieved by adding together the signals from a number of single experiments, in which the experimental radiofrequency phases are varied and the NMR signals combined.

Magic angle spinning is a technique that averages out anisotropic interactions that cause line broadening. If the spinning frequency is not sufficiently high, spinning sidebands occur. They both complicate the spectrum and provide useful information. Methods exist for their suppression and separation, using pulse sequences of carefully-timed π-pulses.

In this thesis, multiplex phase cycling is proposed. In many cases, multiplex phase cycling allows selection of desired coherence pathways using a reduced number of signal acquisitions. By applying different phase factors to the signal in the processing stage, it is possible to obtain signals from different coherence pathways from the same data. The multiplex method is demonstrated experimentally in two-dimensional double-quantum NMR.

Cogwheel phase cycling is a new phase cycling strategy in which the phases of all the pulses are cycled simultaneously. An application of the cogwheel phase cycling to sideband suppression and sideband separation pulse sequences is demonstrated in the thesis. In the case of spin-1/2 nuclei, the cogwheel cycle provides a near seven-fold experimental time saving, while for quadropolar nuclei, the time saving can be up to a factor of hundred.

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