This thesis describes the experimental investigation of the complete resonance absorption spectrum of B¹¹ nuclei in a single crystal of kernite (Na₂B₄O₇.4H₂O) placed in a uniform external magnetic field, and its interpretation in terms of the perturbation of the nuclear Zeeman energy, levels by the interaction of the nuclear electric quadrupole moment with the crystalline electrostatic field gradient. Some observations on the Na²³ spectrum in kernite are also included. The present experiment is one of a series carried out in this laboratory on the study of such nuclear electric quadrupole interactions. In the two previous cases studied, those of Li⁷ and Al²⁷ in LiAl(SiO₃)₂ (spodumene), the atomic positions and symmetry of the crystal are such that there is only one kind of site for each of the two nuclear species studied as far as the electric field gradient is concerned. For both these cases the simplest possible spectrum of 2I lines was observed for any orientation of the crystal with respect .to the erternal magnetic field. In the Li⁷ case first order perturbation theory was adequate to explain the observed spectrum while second order theory was required for the Al²⁷ spectrum. In order to study in detail one case of a complex spectrum due to nuclei of the same species in different non-equivalent positions in the unit cell, the methods of radio frequency spectroscopy used for the previous experiments were applied to the study of the complete B¹¹ [formula omitted] spectrum in kernite (Na₂B₄O₇.4H₂O) in a magnetic field of 7060 gauss. The B¹¹ resonance absorption spectrum was observed in detail as the crystal was rotated about three mutually perpendicular axes. Eleven lines due to B¹¹ were observed when the symmetry axis of the crystal was perpendicular or parallel to the magnetic field, and twenty-one lines were observed in all other orientations of the crystal. In addition to some of these lines were slightly split in some orientations of the crystal. This observed number of lines was interpreted by assuming four essentially non-equivalent boron sites in the crystal with four others obtained from them by a 180° rotation about the b axis of the monoclinic kernite crystal. This interpretation drawn directly from the experimental data is in agreement with the previously proposed symmetry of the crystal on the basis of X-ray data. The complete set of properties of the quadrupole coupling tensor [formula omitted] was determined at each of the non-equivalent B¹¹ sites. The values of the quadrupole coupling constants [formula omitted] at the four essentially non-equivalent sites are .645±.003, .588±003, 2.563±007, 2.567±.010 Mc/s, and the corresponding asymmetry parameters are .54±.01, .60±.02, .163±.010, .116±.010. The orientation of the electric field gradient tensors at the four nuclear sites are given in the thesis. The preliminary investigation of the Na²³ spectrum in kernite leads to a direct contradiction of the positions for these atoms proposed on the basis of earlier X-ray data. Whereas the previously proposed structure postulates three non-equivalent sodium positions, two of which are on axes of symmetry, the Na²³resonance spectrum shows definitely that there are essentially two non-equivalent sodium sites neither of which is on an axis of symmetry. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A new apparatus for the determination of adsorption isotherms is described. The chief feature of this apparatus is that the gas under investigation is allowed to leak slowly, at a known rate, into the adsorbent. The rate at which the pressure increases in the system is recorded. From this data the amount of gas adsorbed by the solid can be calculated and with the measured pressure can be plotted as an adsorption isotherm. The adsorption of carbon dioxide on charcoal has been studied by the use of this apparatus. The reported presence of discontinuities in this adsorption isotherm has not been confirmed. / Science, Faculty of / Chemistry, Department of / Graduate

In this thesis various physicochemical factors which determine the characteristics of latex agglutination immunoassays are examined. A model of antibodies reacting with antigen (bovine serum albumin; BSA) adsorbed to the surface of polystyrene latex (PSL) beads was examined. The adsorption studies of BSA to PSL showed that the mass of BSA adsorbed at saturation depends on the type of polystyrene latex. Latexes with highly hydrophobic surfaces adsorbed more BSA molecules than those with lower hydrphobicity. Desorption studies showed that latexes that maximize adsorption lost the lowest fraction of their bound BSA molecules following extensive buffer wash. Partial desorption of BSA from PSL was achieved by the addition of detergent, whereas the addition of more BSA molecules or other macromolecules such as PEG or IgG did not displace the adsorbed BSA molecules. Examination of the material removed from the surface of the latexes by SDS-PAGE analysis showed that the composition of the adsorbed layer was enriched in the higher molecular weight oligomers of BSA, relative to their concentrations in the stock solution. A model in which adsorbed protein is assumed to undergo a polymerization reaction provides a general explanation of the observed results. Studies of polyclonal antibody (anti-BSA IgG) binding to antigen-coated PSL showed that the surface concentration of bound antibody depends on the surface concentration of antigen on the latex particles and on the availability of PSL surface area not occupied by antigen. Analysis of shear induced aggregation results show that for low surface coverage of latex particles by protein antigen in stable suspension, relatively low concentrations of specific antibodies are required to cause agglutination. Increasing surface density of antigen requires significantly higher concentrations of specific antibodies to produce agglutination. For a given surface coverage of antigen, results show that increasing the shear rate decreases the antibody concentration necessary to produce a given degree of agglutination. A remarkable structure formation and long range ordering exhibited by floes of latex coagulating in salt under intermediate shear rates was observed. This structure formation was not observed during antibody-induced agglutination under shear. / Science, Faculty of / Chemistry, Department of / Graduate

A single Fe³⁺ species has been introduced into Linde L zeolite and is identified as an iron oxyhydroxide from its Mössbauer relaxation properties. The effects of N₂, CO₂ and C₂H₆ on the ferric species and on the bulk behaviour of the sample are observed by Mössbauer Spectroscopy and adsorption studies under outgassing conditions. The ferric oxyhydroxide initially blocks the pores to gas adsorption but reducing it to Fe⁰ at 943⁰ K and reoxidizing it to α-Fe₂0₃ in air at 773⁰ K frees the pores. The bulk α-Fe₂0₃ is concluded to lie on the external zeolite surface. / Science, Faculty of / Chemistry, Department of / Graduate

A systematic study has been done on the absorption and luminescence spectra of transition metal complexes with low-spin electronic configuration d⁶, in order to clarify the spectroscopic behavior of these complexes. The spectra have been measured in solutions and crystals at temperatures between 4 K and room temperature. The lifetimes of the luminescence were measured, too, as an aid to the assignments of the bands. Suitable equipment has been designed and assembled for these measurements. The series of transition metal complexes with different metal atoms and ligands was chosen in order to cover a large range of ligand field strengths and bonding characteristics. Some complexes of Co(lll), Ru(ll), Rh(lll), Os(ll), Ir(lll) and Pt(lV) have been found to luminesce. Other complexes have been investigated and even the absence of luminescence was important for the general understanding of the phenomenon. The results of this investigation show that for the complexes here studied the luminescence originates from the electronic transition ³T₁g, ↦ ¹A₁g , i.e. a transition of d-d type. Also, a luminescence of charge-transfer type has been reported in the literature for some d⁶ complexes. From our data and from the information already-available, some empirical rules were formulated for the luminescence of d⁶ low-spin complexes. A priori use of these rules enables us to prognosticate the presence and the characteristics of the luminescence of other d⁶, low-spin complexes. / Science, Faculty of / Chemistry, Department of / Graduate

The investigation of gas-surface interactions has been approached from two different aspects. Firstly, the design and construction of an apparatus to measure low coverage isotherms for argon on evaporated metal films in the region of liquid nitrogen temperature is discussed. Secondly, a detailed analysis of available second and third order gas-solid interaction data has been carried out. It is found that the existing theories for interpreting and calculating three-body forces in physical adsorption systems are incapable of explaining the observed values. / Science, Faculty of / Chemistry, Department of / Graduate

In this thesis an attempt is made to understand certain experimental results in optical excitation of impurities in semi-conductors. These results are: i) the temperature- and concentration-dependence of the halfwidths of the absorption peaks and ii) the changes in the absorption lines when a compensating impurity is added. These effects are explained by studying the influence (on the neutral absorbing impurities) of the internal fields produced by the ionised impurities. For boron-doped silicon the first effect is due to the inhomogeneity in the field and the second to the quadratic Stark effect produced by the field. An analysis is also presented of the effect on the spectrum of a uniform applied field. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The theory of the phonon broadening of optical absorption lines in impurity doped semiconductors is discussed starting with Kubo's formulation of the adiabatic dielectric susceptibility. The absorption constant is related to a two particle temperature Green's function using Matsubara's method. The interaction of the electrons (or holes) with the lattice vibrations is assumed to be small so that it can be treated as a perturbation to the independent electron and lattice vibration systems. Using this approximation, Dyson equations are obtained, using the technique of Feynman diagrams, for the one particle electron and phonon Green's functions and for the two particle Green's function and these are solved within the framework of the approximation. The line shape function is calculated explicitly and it is found that the line consists of a sharp peak whose width depends on temperature and is due to the finite lifetime of the bound carrier states, and of a continuous background due to multi-phonon processes which accompany the optical absorption. The technique used here is compared with previous work on this problem employing temperature dependent double-time advanced and retarded Green's functions. The results obtained are compared with those obtained by previous authors. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In uncompensated phosphorus or arsenic-doped silicon, observation of the shallow, donor absorption line spectrum for donor concentrations from 10(12) to 2 x 10(18)/cc, yields information about the bound states of the donor electrons and the behavior of the conduction band edge. With increasing concentration, the photon induced IS(A) → 2P(o) and IS(A) → y 2P(±) transition lines are observed to broaden in energy, and shift to slightly lower energies; the lineshapes, Lorentzian at low donor concentrations, become asymmetric with the formation of a tail to the low energy side. A superposed absorption background is observed for donor concentrations greater than 2 x 10(16)/cc. Above 2 x 10(17)/cc an absorption edge in the 10-to-30 meV region with an exponential energy dependence is observed. The change in the absorption line spectrum is due primarily to the final states. The halfwidths of the transitions are well explained by a donor-pair model (or effective hydrogen molecule (Macek, 1971)), with the donor distribution assumed random. The difference in broadening of the 2P(±) level compared to the 2P(o) level is due to the anisotropic effective mass of the donor electron. The transition lineshapes are quantitatively explained in terms of the convoluted Fano function (Bhatia, 1970; Fano, 1962). The Fano parameters Q and T, are interpreted in terms of the evidence for the conduction band tailing and the possible configuration interaction. The integrated absorption coefficient of the line spectrum and the decrease of the absorption cross section above the conduction band threshold with increasing concentration are also accounted for in terms of band tailing. The experimental results are in agreement with the infrared absorption data for antimony-doped germanium (Nisida and Horii, 1969). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The presence of configuration interaction, between the "internal" acceptor states of group III impurities in silicon and P₃⁄₂ band Bloch states, has been observed. The effect of impurity-impurity interaction on the line shape of the boron, gallium and indium internal acceptor lines has been studied. The observed characteristic asymmetric line shape is explained by introducing the interaction of the internal state with the degenerate P₃⁄₂ valence band Bloch states, and the inhomogeneous impurity-impurity interaction. The ionization energy of the substitutional impurity in the host lattice is found to be a deciding factor in this interaction. The internal and external absorption spectra of silicon doubly-doped with boron and indium acceptors is studied. The observed broadening of the boron external absorption lines in Si(B,In) is explained by neutral impurity scattering. The presence of indium in Si(B,In) crystal lattice, modifies the P₃⁄₂ valence band Bloch states and hence the configuration interaction. This modification is found responsible for the observed features of the boron 2p′ internal line in Si(B,In). The coupling between the lattice and the impurity bound carrier for deep monovalent acceptors in silicon, such as gallium and indium, is found to be stronger than for the shallow boron impurity. This suggests the possible existence of phonon-assisted transitions associated with these deep impurities. Such transitions are observed in the absorption spectrum of indium doped silicon. The phonon-assisted transitions are superimposed on the photoionization continuum transitions of the indium acceptors. Interference effects between the phonon-assisted transition and the transitions to the continuum states modify the position and line shape of the transitions. Using the phonon dispersion curves for silicon, interpretation of the results is presented. As a supplementary study, the temperature dependence of the indium external line 2, is investigated. The temperature dependence of halfwidth of indium line 2 in Si(In) supports the stronger electron-phonon coupling in Si(In). / Science, Faculty of / Physics and Astronomy, Department of / Graduate