Thesis (M.Sc.)(Chemistry)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

An experimental technique has been developed for the investigation of departures from thermodynamic equilibrium in plasmas. The relative populations of the upper and lower levels of a spectral line are measured by the reversal temperature method. The reversal temperatures themselves are determined by varying the relative exposure times of the background source and the plasma to be investigated. The relative population densities of the levels in the 2p⁵3s and 2p⁵3p configurations of Nel have been measured. A Neon glow discharge operated in the current region 1mA to 100mA served as the plasma. The results show that the excited gas is definitely not in thermal equilibrium. The relative intensities of the emission lines between the 2p⁵3s and 2p⁵3p configurations of NeI were measured photometrically and corrected for self-absorption. These intensities were then used in conjunction with the relative population densities to determine relative transition probabilities for the spectral lines concerned. The results are accurate to approximately 10% to 15% and are compared to the values obtained previously by other workers. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Spectroscopic measurements were made on plasmas in electromagnetic shock tubes to test the state of equilibrium in these plasmas. In an Argon-Oxygen mixture the relative intensities of AII and AIII lines and of OII lines indicated that complete equilibrium was not established. In a Helium plasma the observed line intensities showed that the populations of the Hel levels agreed with a Boltzmann equilibrium distribution. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Previous work by Heal had shown that X-irradiated sodium azide crystals dissolved in water produced small amounts of nitrogen gas, hydroxyl ion and ammonia, thereby indicating that some decomposition had occurred. Heal also observed colours in the material, similar to those of the X-irradiated alkali halides for which a whole series of colour centres responsible have been postulated. It was therefore decided to investigate the colour centres of the alkali azides, partly to extend the colour centre research, and partly to illuminate the X-ray decomposition processes. Crystalline plates of NaN₃, KN₃, RbN₃ and CsN₃ were irradiated at liquid nitrogen and room temperature, using a Machlett AEG-50 tungsten target X-ray tube, operated at 50 KVP. The absorption spectra of the irradiated samples were measured at liquid nitrogen temperature with a Cary model 14 recording spectrophotometer. The low temperature spectra consisted of three bands. The A band, peaking at 612, 568, 578 and 592 mu for NaN₃, KN₃, RbN₃ and CsN₃, respectively, is ascribed to F centres. The anomalous sodium azide band is related to its trigonal crystal structure, differing from the body centred tetragonal of the other azides. The B band, peaking at 361, 374 and 390 mu for KN₃, RbN₃ and CsN₃ respectively, was strong and triple, there being shoulders about 30 mu on each side of the main peak. For NaN₃ it was weak, single and peaked near 330 mu. Tentatively, it is ascribed to the centre. The C band, peaking about 740, 790, 820 and 850 mu for NaN₃, KN₃, RbN₃ and CsN₃ is weak and single. It may be due to F1 centres. The room temperature spectra were strikingly different from each other, except for RbN₃ and CsN₃. For NaN₃ five bands were observed at 342, 560, 630 , 730 and 860 mu; the latter four were weak and may be an electronic vibrational spectrum. The strong 342 mu band is ascribed to the presence of sodium metal in some non-colloidal form; a correlation between the band and the ionisation potential of the metal is noted. In KN₃ three bands at 760 (strong), 590 (strong shoulder) and 340 mu (weak) were obtained. The first two are ascribed to small F centre aggregates of the M,R type though no definite assignations are made. RbN₃ and CsN₃ spectra both consist of a broad peak showing fine structure, the highest peaks occurring at 330 mu and 375 mu respectively. It is considered uncertain that all the absorption is due to the impurity held responsible for the fine structure. / Science, Faculty of / Chemistry, Department of / Graduate

The theory of the Raman Effect in crystals has been re-examined by O. Theimer (Can. J. Phys. 1956, 34 312) in an attempt to overcome some discrepancies between experimental results and predictions of the theory. New selection rules have been derived by investigating the validity of the assumptions made in the earlier theory. The new theory, applied to the symmetric Raman line of Calcite, predicts that, for the crystal orientated with its optic axis parallel to the illuminated surface, the "forbidden" component will be truly forbidden for forward or backward scattering, while appearing as previously reported for scattering at 90°. The present investigation is concerned with measuring the relative intensities of the polarized components of this line for backward scattering, the measurements being made with the crystal orientated with its optic axis either parallel or perpendicular to the illuminated surface. A method for increasing the scattering volume by joining several crystals along cleavage faces has been developed and a new mercury discharge lamp was designed which gave an appreciable increase of the illumination intensity. The relative intensities of the components of the symmetric Raman line obtained were evaluated by careful consideration of the characteristics of the photographic emulsion used to record them. The results tend to confirm the predictions of the new theory. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The adequacy of the approximation method used by McMillan and Opechowski (1960) in their theoretical study of the temperature dependence of the paramagnetic resonance line shape function is very difficult to ascertain for the case of a typical paramagnetic crystal. For this reason the approximation method has been investigated, in this thesis, for the very simple case of the one-dimensional Ising model. Exact expressions for the line shape function of the model are compared with expressions obtained by the above mentioned approximation method. The agreement between the two expressions is found to be very good for all temperatures, and in particular, for extremely low temperatures. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The spectra emitted by a pulsed-arc discharge have been photographed with a medium resolution spectrograph to obtain Stark broadened line images measurable for both width and shift. Plasmas with densities near 10¹⁷cm⁻³ and temperatures of about 2.6 ev were produced by subjecting Argon - Nitrogen mixtures to a square current pulse. Light from the discharge was shuttered by a rotating mirror system so that the plasma was photographed in an interval during the current pulse when the plasma had optimal conditions for measurement. A technique in which the spectral lines from a standard source are photographed on the same plates as the plasma lines has been devised for calibrating the measurement routine and for facilitating shift measurements. Stark parameters were obtained by scanning the plates on a precision comparator. Nineteen ArII lines and six NII lines were studied. For Argon, the agreement with other experimental results is satisfactory but the theory is inadequate. Similarly, the NII theory does not predict the values measured here. On the other hand, some of the qualitative predictions by the Impact theory about the line shape and about the common widths and shifts of lines in the same multiplet have been confirmed. The experiment on the NII lines also reveals advantages of the present technique over other methods for obtaining Stark parameters. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A new experimental technique has been developed for the determination of absorption line profiles in steady-state plasmas. The method involves observing the total transmitted line intensity of one component of the longitudinal Zeeman pattern from a background source. The frequency shift of this line is determined from the known magnetic field and the Landé g-factors involved. The light from the background source is amplitude modulated by a chopping wheel, and the intensity of the transmitted light is measured with a phase-sensitive detector. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Photoelectron spectroscopy is the study of the kinetic energies of the photoelectrons ejected from gaseous species by monochromatic radiation. Subtraction of these kinetic energies from the incident photon energy yields the binding energies of the orbitals from which the electrons were removed. The work to be described falls into two main parts. The first is concerned with the development of a new type of spectrometer to measure such kinetic energies. To date, all photoelectron spectrometers designed specifically for gaseous samples have employed a retarding field of cylindrical geometry to energy-analyze the emitted photoelectrons. Consideration of the angular distribution with which electrons are ejected during the photoionization process indicates that a spectrometer utilizing a retarding field of spherical geometry should give a stopping curve, the first differential of which is close to the true photoelectron kinetic energy spectrum. Instruments of both cylindrical and spherical geometry were constructed and their properties tested. Conclusive evidence for the superiority of the spherical system is presented together with details of its construction and operation. The second part of this thesis/contains the results of photoelectron spectroscopic studies on twenty-one atoms and molecules (Ar, Kr, Xe, H₂, HD, D₂, N₂, CO, O₂, NO, HF, HCl , HBr, HI, F₂, Cl₂, Br₂, I₂,N₂O, NO₂ and NH₃). The energies of the ionic states could be obtained to a precision of 0.01 ev., and they agree, well with available spectroscopic data. In many instances new ionic states are found, and where possible they are correlated with states predicted by molecular orbital theory. Relative transition probabilities to the various ionic states are also obtained by this method. They are, in nearly every case, the only experimental values available. The spacings and relative probabilities for formation of ionic vibrational levels have been measured for certain states in H₂, HD, D₂, N₂, CO, O₂, NO, F₂, N₂O and NO₂ and the values obtained compared with spectroscopic and calculated data where this is available. / Science, Faculty of / Chemistry, Department of / Graduate

A study involving both the applications of internuclear double resonance (INDOR) spectroscopy and the synthesis of carbohydrates containing organometallic substrates was undertaken. The thesis is divided into two sections to facilitate discussion. The first section involves an evaluation of homonuclear and heteronuclear INDOR as a tool for spectral analysis. Homonuclear INDOR studies of carbohydrate derivatives such as 2-deoxy-a-D-arabino-hexo-pyranose(l), sucrose octaacetate(2) and D-ribose(3) have shown this technique to be extremely effective for analysing multi-line spectra having hidden transitions. Within certain power-level ranges, the resolution of the INDOR responses is comparable to that of the normal proton spectra. Heteronuclear INDOR spectra were obtained indirectly by monitoring specific transitions in the proton spectra while irradiating the appropriate heteronuclear frequency. In this manner, the methoxy-methyl ¹³C INDOR shift of a number of anomeric gluco- and xylo-pyranoside derivatives were measured. The ¹³C shifts of the α anomers were found to be ca. 2 ppm to high field of the β anomer. This difference is more diagnostic than the small 0.1 ppm variation between two methoxy-methyl anomers in the ¹H n.m.r. spectra. Such diagnostic differences were not found for the acetoxy-methyl ¹³C shifts of anomeric sugar acetate derivatives. Other heteronuclear INDOR spectra were readily obtained for organo-metallic compounds such as trimethylphosphite(15), trimethyltin chloride (16), bromosilane(17) and tetramethyl lead(18). The second section of the thesis deals with the synthesis of some phosphorus and organometallic derivatives of monosaccharides. Treatment of various primary O-tosyl sugar derivatives with lithium diphenyl-phosphine reagent ,19, gave, in ca. 70% yields, such products as diphenyl {1,2 :3,5-di-0-methylene-α-D-glucofuranose} 6-C-phosphine oxide(20b), diphenyl {methyl 2,3,4-tri-0-acetyl-α-D-glucopyranoside} 6-C-phosphine oxide(21b) and diphenyl {l,2:3,4-di-0-isopropylidene-α-D-galactopyranose} 6-C-phosphine oxide(22b). The facile preparation of 22b is rather unique because of the known resistance of the O-tosyl group of the sugar reactant toward nucleophilic displacement. Diphenyl {3,6-anhydro-l,2-0-isopropylidene-α-L-idofuranose} 5-C-phosphine oxide(24b) was obtained in 31% yield via nucleophilic displacement of the corresponding 5-0-mesyl derivative using 19_. This typified the much lower yields obtained from secondary sulphonyl displacements. Other secondary sugar diphenyl-phosphine oxide derivatives were prepared in 50-70% yields from the opening of sugar epoxides with 19_. Notably, the scission of the epoxide bond of methyl 2,3-anhydro-3-L-ribopyranoside(29) gave diphenyl ^methyl 2,4-0-acetyl-B-L-xylopyranosidej. 3-C-phosphine oxide(30). The product was found to favour the conformation in which all the major substituents are axial. The ³¹P chemical shifts for all the sugar diphenylphosphine oxide , derivatives were measured using the INDOR technique. These shifts provided confirmation that the products were phosphine oxides. It was further shown by use of ³¹P decoupling that ³JpH ranges of 6.6-11.8 Hz and 22-33 Hz for 60° and 180° dihedral angles respectively, were present in these products. These couplings are similar to those reported for, vicinal P-H couplings in hydroxy phosphonate derivatives. Preliminary experiments, undertaken to evaluate the effectiveness of other organometallics such as lithium triphenyltin(33), lithium tri-phenyllead(34) and lithium triphenylsilane (35) , showed 33 to be an effective reagent for displacing primary O-tosylates and opening epoxides of sugar derivatives. Both 34 and 35 gave poor yields when used to displace the 0-tosylate group of 20b. Generally, organometallic species were shown to provide a viable means of synthesizing novel sugar derivatives. / Science, Faculty of / Chemistry, Department of / Graduate