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The binding energies and momentum distributions of all of the valence orbitals of (CH₃)₂O, PH₃, CH₄ and SiH₄ have been measured by high momentum resolution electron momentum spectroscopy. The binding energy spectra have been compared to Green's function and configuration interaction calculations from the literature and with new calculations performed in collaboration with co-workers at Indiana University and Universitat Braunschweig. For PH₃, CH₄ and SiH₄, near Hartree-Fock limit calculations of the momentum distributions and very accurate calculations of the ion-neutral overlap using MRSD-CI wavefunctions to describe the ion and target have been performed in collaboration with co-workers at Indiana University. Good agreement is obtained between the (CH₃)₂O measurements and the momentum distributions calculated from relatively simple wavefunctions, except in the case of the outermost orbital. The effects of diffuse and polarization functions in the basis sets, and also the influence of molecular geometry, have been investigated. Comparison of the momentum distributions of the outermost orbitals of H₂O, CH₃OH and (CH₃)₂O demonstrates a delocalization of charge density with methyl substitution. The measured momentum distributions of PH₃, CH₄ and SiH₄ are compared with near Hartree-Fock limit calculations as well as ion-neutral overlap calculations in which the ion and neutral wavefunctions are described by multireference, singly and doubly excited, configuration interaction calculations. In each case, the experimental results are well modelled by the near Hartree-Fock limit calculations, and there is little difference between the Hartree-Fock limit and ion-neutral overlap calculations. A significant splitting of the 4a₁ (inner valence) pole strength is observed for PH₃, but the inner valence strength is largely contained in the main peak for both CH₄ and SiH₄. Green's function calculations quantitatively reproduce these results. Ion-neutral overlap calculations using MRSD-CI wavefunctions to describe the ion and target have been performed for HF, HCl, Ne and Ar. These are compared with previously published EMS measurements of the momentum distributions. Very poor agreement between theory and experiment is obtained for HF and HCl. The theoretical and experimental results for all of the hydrides CH₄-HF and SiH₄-HCl as well as Ne and Ar are reviewed. / Science, Faculty of / Chemistry, Department of / Graduate

A wide variety of inelastic scattering and electron attachment phenomena have been studied by directing an electron beam into a gas filled chamber and by observing the results of the interaction. The use of a "monoenergetic" electron beam has permitted the relative cross sections for such processes to be examined in some detail. Three instruments were used to make the measurements, and these instruments were designed and constructed during the course of the work to be described. All three employed a 127° electrostatic electron velocity selector to filter the electron beam. An electron energy analyzer permitted the observation of inelastically scattered electrons, and a monopole or a quadrupole mass filter permitted the measurement of the relative amounts of positive or negative ionization generated by the electron beam in its interaction with the gas. The measurement of the energy dependence of the cross sections was the prime objective of the work, and much care was taken in the design of the instruments to ensure that the cross section curves were not distorted by spurious effects. The forward inelastic scattering spectra of helium and ethylene were recorded using an electron beam having an incident energy of 50 eV . The ionization efficiency curves of singly and doubly charged helium were obtained, and the results are compared with several theoretically derived expressions for electron impact threshold laws. The positive ionization efficiency curves for nitrogen and oxygen were also obtained. An examination of the dissociative capture, non-dissociative capture and ion pair processes has been made by determining the energy dependence of the cross sections for the production of the parent and/or fragment negative ions from nine molecules. Finally, the generation of zero energy electrons from inelastic scattering events has been studied by using sulfur hexafluoride as an electron scavenger in a mixture with the sample gas. The threshold electron impact spectra were obtained for six atomic and molecular species. In all cases, such measurements were carried out below and above the ionization potential of the sample. / Science, Faculty of / Chemistry, Department of / Graduate

Electron paramagnetic resonance techniques have been used to investigate the nature and possible effects of adsorption of gaseous species on several adsorbents, in particular several synthetic zeolites, at temperatures from 77°K upwards. Analysis of the spectra obtained has been aided through computer simulation of the various spectra and comparison of these to the actual observed spectra. The molecule chlorine dioxide ( C10₂ ) has been studied in various low temperature matrices but little has been published for C10₂ in the adsorbed state. An attempt was made to find an adsorbent such that an inert matrix might be approximated, to give a base from which to make comparisons. To this end, adsorbents including silica gel, synthetic zeolites 13X, 10X, 4A, 5A, Na-mordenite and H-mordenite were investigated. The results vary between those from silica gel, where spectra yielding EPR parameters similar to other matrices were obtained, to those from 13X where it was evident that two distinct adsorption sites of the C10₂ were present. In the 13X as in the other synthetic zeolites, EPR parameters markedly different from other studies were found and were attributed to the intense electrostatic fields present in these zeolites. Results obtained at room temperature for these adsorbents ranged from C10₂ molecules freely rotating in the cages of the zeolites to other molecules having hindered rotations. Nitrogen dioxide ( NO₂ ) was also investigated with a view to finding similar interactions. Although changes as marked as for C10₂ compared to other studies were not observed, the synthetic zeolite H-mordenite yielded spectra closely approximating those obtained in solid N₂O₄ matrices. It is proposed the NO₂ molecules are caged in the numerous side pockets emanating from the main channels in this zeolite and are effectively isolated from other NO₂ molecules. The resulting spectra are strikingly more resolved than those obtained using other adsorbents and enabled accurate computer simulations to be made. The adsorption of nitric oxide ( NO ) produced an effect not found with the other molecules. A new species was formed from a reaction of the NO with H-mordenite and could not be removed at room temperature, indicating a strong bond to the surface. The new species does not contain nitrogen as identical spectra were obtained from adsorption of ¹⁴NO and ¹⁵NO. Attempts to observe spectra which could be assigned to the difluoroamino radical from adsorption of tetrafluorohydrazine were unsuccessful. The spectra observed were assigned to a species having no hyperfine structure and an anisotropic g tensor. / Science, Faculty of / Chemistry, Department of / Graduate

Paramagnetic impurities containing oxygen were produced in the reactions of KBr, KCl, NaCl and SrCl(2) with fluorine. Molecular oxygen, FOO･ radical and C10(2) were identified by ESR as reaction by-products. The spectra assigned to CIO(2) have predominant powder character even in single crystals of halides. The results are correlated with previous work in this laboratory. The origin of oxygen impurity is suggested to be surface hydroxide ions in KBr and KC1, and entrapped water in NaCl and SrCl(2). Nucleation processes and other anomalous features observed in these reactions by previous workers are explained by the presence of impurities. Oxygen was found to be incorporated into the SrCl(2) crystals by recrystallisation from the melt in the presence of oxygen. It exists in the form of superoxide ion O(2)¯ which occupies an interstitial position between two lattice anions and is associated with two anion vacancies. The molecular axis lies in a [00l] direction of the crystal and the degeneracy of the 2pπ(g) -molecular orbital is lifted by the crystal field. The bonding between the O(2)¯ ion and its neighbouring cations and anions is discussed in terms of a Cl(6)Sr･O(2)¯･SrCl(6) "complex". The orbital angular momentum reduction factor for O(2)¯ in SrCl(2) has been calculated from the experimental g-factors and found to be anomalously large. A survey was made on impurities incorporated into strontium compounds through processes of recrystallisation from melts or from aqueous solutions. Strontium carbonate was identified in melt-recrystallised Sr(NO3)(2) by Infrared Spectroscopy and X-ray powder method. It was produced by partial decomposition of the nitrate in the presence of atmospheric CO(2). NO(3)²¯ ion was identified in the recrystallised material by ESR. ESR and infrared studies suggest that the NO(3)²¯ ion substitutes a carbonate ion in the SrCO(3) lattice. Results from a similar study on Ba(NO3)(2) also support this conclusion. / Science, Faculty of / Chemistry, Department of / Graduate

X-irradiated cyanoacetylurea CNCH₂CONHCONH₂ and x-irradiated dicyandiaraide NCNC(NH₂)₂ single crystals were studied,by Electron Spin Resonance. Two radical species were formed when cyanoacetylurea, CNCH₂CONHCONH₂, was irradiated with x-rays. One was a π-electron radical, CNCHCONHCONH₂, and the other a σ-electron radical, CNCH₂CONHCONH . The σ electron radical was found to have a large, isotropic proton coupling tensor and an anisotropic nitrogen coupling tensor very similar to those of H₂NCOCH₂CONH . The π-electron radical had similar proton and nitrogen coupling tensors as CNCHCOOH which was formed in γ-irradiated cyanoacetic acid. In x-irradiated dicyandiamide crystals, the main species formed was shown to be NCNC(NH₂)NH, having also a large, isotropic proton coupling tensor, and hyperfine interactions with two nitrogen coupling nuclei were also observed and measured. ESR studies were carried out both at room and at liquid nitrogen temperatures. The effect of temperature on the spectra is discussed. INDO-SCF-LCAO-MO calculations were carried out for a model compound HCONH , with the amide proton assuming different inplane and out of plane positions. The spin density was found to vary over a wide range and could be used to interpret the large proton coupling of the dicyandiamide radical. MO calculations were also performed on the radical NCCHCOO ̄. The calculated results correlate fairly satisfactorily with the observed ones. Comparison of the direction of the unpaired electron p-orbital symmetry axis with bond directions and with normals to the fragment planes showed that while malonamide radical, H₂NCOCH₂CONH was a genuine σ-electron radical, dicyandiamide radical, NCNC(NH₂)NH was most likely a π-electron radical. / Science, Faculty of / Chemistry, Department of / Graduate

The e.p.r. spectrum for relatively dilute samples of phosphorus-doped silicon (<5 x 10(16) donors/cm³) has been calculated in detail for an assumed random distribution of impurities. The system of donor electron spins is treated as a collection of nearest neighbor donor pairs. An expression is derived for the donor pair exchange energy using Kohn-Luttinger wavefunctions and a general exchange energy expression. The resultant relationship contains an adjustable parameter a*, the "effective Bohr radius", which is determined from a comparison of the calculated spectrum and the experimental results obtained for the ratio, C, of the "central pair" and "hyperfine" line intensities. The resulting expression J(R), where J represents the exchange energy and R the separation vector connecting the two pair donors, exhibits an oscillatory spatial dependence due to interference from portions of the wavefunction arising from different conduction band valleys. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A completely general method has been developed for calculating Electron Paramagnetic Resonance (EPR) transition fields and transition probabilities from the spin Hamiltonian [formula omitted] The method is a generalization of a previously existing, limited technique, and can be applied without any restrictions. A general computer program has also been written based on the method. Using the program, the results of an EPR study on a U.V. irradiated single crystal of para-nitrophenyl azide were fitted to the spin Hamiltonian [formula omitted] The observed and calculated fine and hyperfine transition probabilities were found to be in good agreement. The observed hyperfine splittings, due to the nitrene nitrogen, were analyzed in terms of a 6.5 gauss linewidth, combined with the transition probabilities for the nine theoretical components of the hyperfine resonance fields. Evidence of a ¹⁴N quadrupolar splitting was observed, but not completely analyzed. In addition, evidence was found to indicate that the nitrene impurity is twisted somewhat from the position in the crystal lattice held by the parent azide. The EPR spectra obtained on U.V. irradiation of randomly oriented 1,5- and 1,8-diazidonaphthalene were analyzed, and found to originate from ground triplet state species with |D|= 0.8152±0.0010 cm⁻¹ and 0.7599±0.0010 cm⁻¹, respectively. The theoretical spin densities for the triplet and quintet states of 1,5- , 1,8- and 2,7- naphthalene dinitrene were calculated using the method of intermediate neglect of differential overlap (INDO). Attempts to obtain a consistent picture of multiplet spin densities based on the results of the calculations were largely inconclusive. / Science, Faculty of / Chemistry, Department of / Graduate

Lattice misfit and its effect on the morphology, interfacial structure and kinetics of plate shaped precipitates are investigated in this study. The 7-Ag₂Al phase in the Al-Ag system was used as the reference system and its misfit was controlled by ternary additions of Mg and Cu. The addition of 0.S1 at% Mg was found to increase the misfit from 0.8% for the binary to 1.11%. Cu additions on the other hand, reduced the misfit by 0.38% for Cu concentrations up to 0.51 at%. Electron probe microanalysis showed that the Mg atoms preferentially partition to the 7 phase whereas Cu atoms partition equally between the precipitate and matrix phases. Direct transmission election rnicroscope observations were made on the interface structure in both the equilibrated state and during precipitate dissolution. The interface structure in the ternary Mg alloy consisted of a hexagonal network of partial dislocations which essentially remained the same before and during dissolution. A single array of a/2<110> dislocations was observed in the binary and ternary Cu systems prior to dissolution. This unit array transformed to a stable hexagonal network structure having the equilibrium spacing at the onset of dissolution and remained throughout the period of dissolution. The thinning and shortening kinetics of the precipitate plates were at least five times slower than the rates for volume diffusion control in all three systems. This interfacial inhibition has further been confirmed by the consistent fall below equilibrium values of the interface concentration as determined from electron probe microanalysis. This suggests the operation of a ledge migration mechanism. A mechanism of acquiring ledge/dislocations at the interface is used as a basis to correlate the observed kinetics with misfit and ledge migration at the precipitate-matrix interphase. The mechanism involves co-ordinated motion of sets of dislocations in the network which rids the surface of the highest steps thereby accomplishing dissolution. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate