Nuclear magnetic resonance in isopentane at low temperatures

Abstract

Nuclear Magnetic Resonance depends for its existence on the fact that most nuclei of the elements exhibit gyromagnetic properties. These properties were first attributed to the nucleus by Pauli (1921) to explain hyperfine structure in atomic spectroscopy. When a sample containing nuclei exhibiting gyromagnetism is placed in a magnetic field, and is irradiated by an appropriate rotating radio-frequency magnetic field, the nuclei can be compelled to reveal their presence, identify themselves, and to describe the nature of their environments. Such experiments can, amongst other things, yield evidence of crystal and molecular structures, hindered molecular motions, and thermal relaxation mechanisms. This thesis is concerned with such effects. Rabi, Millman, Kusch and Zacharias (1939) first applied the resonance method to individual atoms and molecules in atomic beam experiments, and produced transitions between the quantised nuclear magnetic energy levels by a process of absorption or stimulated emission. Gorter had shown that this resonant exchange of energy should not be restricted to molecular beams, but should also be observed in matter in other forms in which internolecular interactions would occur. Gorter (1936), and Gorter and Broer (1942) unsuccessfully attempted to detect energy absorption by ⁷Li nuclei in Li F. It was later shown by Gorter (1931) that the failure was mainly due to the use of unfavourable materials The first successful experiments of nuclear magnetic resonance in bulk material were made simultaneously and independently by Purcell, Torrey and Pound (1946), and Bloch, Hansen and Packard (1946). The development of the subject since these pioneer experiments has been such that applications have been found in many branches of physics and chemistry. Several companies now manufacture Nuclear Magnetic Resonance spectrometers, and these have achieved equality in importance with infra-red and mass spectrometers in many chemical research laboratories.