Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.631068
Title: Some novel developments in high-resolution NMR spectroscopy
Author: Odedra, Smita
ISNI:       0000 0004 5355 4031
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2014
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Abstract:
The radiofrequency (rf) pulses used in NMR are subject to a number of imperfections, such as those resulting from the inhomogeneity of the rf field or an offset of the transmitter frequency from exact resonance. In spin-echo experiments, these imperfections yield spectra with reduced signal intensity and distorted phase. Composite pulses, which have tailored bandwidth properties with respect to experimental frequency parameters such as the rf field strength or resonance offset, offer a route to improving the amplitude of the spin-echo signal. However, the symmetry of the pulse sequence must be carefully considered to prevent the introduction of phase errors into the spin-echo signal. Here, composite pulses will be studied as a means to improving one of the most common techniques for 1H background suppression in MAS NMR, the ”Depth” sequence. Novel composite 180° pulses will be presented for this application and verified experimentally. The composite pulse Depth experiment yields spectra with improved amplitude of the 1H signals of interest, while successfully maintaining good suppression of background signals. Novel families of dual-compensated 180° composite pulses for I = 1/2 will also be designed for use in NMR spin-echo experiments. These pulses are capable of simultaneously compensating for resonance offset and rf inhomogeneity problems. Crucially, unlike many composite pulses that have been presented before, these new pulses have the correct symmetry properties to form a spin echo without phase distortion. Composite pulses have found wide usage in solution-state NMR, and although in principle the same pulses can be applied in solid-state NMR experiments, complications can arise under magic angle spinning (MAS). The effects of MAS on composite pulse performance will be explored both through computer simulations and 31P experiments. Finally, on a different theme, we will investigate spin-locking of half-integer quadrupolar nuclei in solids. Spin-locking is an important feature of many NMR experiments, yet the complex behaviour observed for quadrupolar nuclei is not fully understood. Using the theoretical model introduced by Ashbrook and Wimperis, we will investigate the far off-resonance case of spinlocking for I = 3/2 and I = 5/2 nuclei.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.631068  DOI: Not available
Keywords: QC Physics ; QD Chemistry
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