The work described in this thesis was performed at the Physics Department, Rhodes University during 1958 and 1959 under the supervision of Professor J.A. Gledhill. Use was made of a vacuum ultra-violet spectrograph which had been constructed in the Physics Department (1.1) and modifications to be described were made to this instrument. The instrument was used for studying the effects of oxygen on the fluorescence excitation spectrum of Anthracene.

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In this thesis, Molecular Dynamics simulations of shocked single crystals of Copper and Iron are studied using simulated X-ray diffraction. Strains and volumetric compression in modeled Copper crystals shock-compressed on picosecond time-scales are found. By comparing the shifts in the second and fourth diffraction orders, the density of dislocations is calculated. In Iron, simulated X-ray diffraction is used to verify the modelling of the α-ε phase transition induced by shock-compression on picosecond time-scales. No plastic deformation of Iron is found in the studied pressure range of ~ 15-53 GPa. The results are then compared with data from in situ X-ray diffraction experiments of laser-shocked single crystals. Near-hydrostatic compression of shock-compressed Copper on nanosecond time-scales is confirmed using a new wide-angle film diagnostic capturing diffraction from multiple crystal planes. Also, the first in situ X-ray diffraction evidence of the onset of the α-ε phase transition in laser-shocked single crystal Iron is shown. No plastic yield of the crystal lattice is found, which is in agreement with the simulation results. Results from both the Molecular Dynamics simulations and experiments are used to suggest enhancements in computer modelling of shocked crystals, as well as future experimental studies. In particular, the need for a measurement of dislocation densities during the shock wave passage through a crystal is highlighted, and a method enabling such a measurement is proposed.

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A detailed study is made on the luminescence of Pb('2+) ions in alkali halide single crystals. The emission spectra of KX:Pb('2+) (X = Cl, Br, I) excited in the A-absortpion band at various temperatures are reported. In addition, the excitation spectra of the A-band emission measured at 4.2 and 78 K are also given. The temperature dependence and the effect of an external magnetic field on the decay time of the A-band emission from KX:Pb('2+) is also investigated. / The results are interpreted in terms of a model that includes the Jahn-Teller effect, the spin-orbit interaction and an additional perturbation caused by the charge compensating cation vacancy (CV, v(,c)('-)). In this model, the Jahn-Teller effect is much smaller than the spin-orbit interaction and the CV is smaller still. The experimental results for KX:Pb('2+) are well in accord with this model. / The angular dependence of the polarization of the A-band emission from KX:Pb('2+) confirms that the Pb('2+) - v(,c)('-) pair is located on the C(,4) crystallographic axis. The temperature dependence of the polarization is treated within the framework of the above model in terms of the nonradiative processes between the relaxed excited states.

The chiroptical properties of isotropic solutions, cholesteric liquid crystals and solid films prepared from selected cellulose derivatives are investigated by optical rotary dispersion (ORD) and circular dichroism (CD). Optical activity from intrinsic molecular dissymmetry, polymer conformation and cholesteric reflection properties are considered. / The chiroptical properties of cholesteric liquid crystals are interpreted according to deVries' theory. Lyotropic liquid crystalline phases formed by (hydroxypropyl)cellulose in methanol display anomalously high optical rotation at low wavelengths. The anomalies disappear on the addition of a dipolar aprotic solvent, and are absent for the ethyl ether derivative of the polymer, indicating a chiral hydrogen bonded structure is contributing to the optical activity. / Investigation of the chiroptical properties of cellulosics by circular dichroism requires the presence of a suitable chromophore, either as a chain substituent or as an added dye. Congo red exhibits induced optical activity in dilute aqueous solutions of methylcellulose and cellulose oligomers, providing evidence for the presence of a helical conformation. CD spectra of two new biphenyl derivatives also exhibit exciton splitting characteristic of a helical arrangement of chromophores. Conformational dissymmetry is not indicated in spectra of cellulose acetate although the sign of carbonyl CD band is solvent dependent. The sign of this band is interpreted in terms of the orientation of the ester substituent relative to the anhydroglucose ring. Congo red, bound in cholesteric cellulose films prepared by the deacetylation of cellulose acetate cast from mesophase solution, shows induced optical activity which, in this case, reflects the cholesteric nature of the matrix. Similar results for cellulose gels regenerated from LiCl/N,N-dimethylacetamide solution indicate that cellulose adopts a supramolecular helicoidal arrangement on slow precipitation from solution. / The optical properties of the thermotropic cholesteric liquid crystalline phase formed by a new cellulose derivative, (ethoxypropyl)cellulose, are examined by circular reflectivity measurements. / The cholesteric reflection properties of mesophase solutions of cellulose acetate in trifluoroacetic acid are characterized. The polymer undergoes rapid trifluoroacetylation in this solvent and the presence of trifluoroacetate substituents alters the handedness and the magnitude of the pitch. Although the pitch is sensitive to the nature of achiral substituents, it is not influenced by the addition of chiral solvents. (Abstract shortened with permission of author.)

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