Hexagonal close packed and cubic close packed structures of heavy rare gas atoms are compared. Lattice expansion effects are examined for a model in which atoms interact via Lennard-Jones (12-6) potentials, lattice motion is according to the quasiharmonic approximation, and the model crystals are in equilibrium at constant temperature and pressure. Phonon frequencies are found to depend sensitively upon lattice parameters. In the cubic (hexagonal) structure the phonon modes most strongly affected by expansion are long (short) wavelength, longitudinal (transverse), acoustic (optic) modes. Phonon frequencies for the cubic structure all remain real for expansions considerably greater than would cause imaginary frequencies for the hexagonal structure. Equilibrium lattice parameters are found to deviate from their static equilibrium values by amounts depending upon the De Boer parameter, the deviations being slightly greater for the hexagonal structure, which exhibits nonideal stacking. The problem of explaining the observed stability of the cubic structures of real rare gas solids is discussed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (Ph. D.)--York University, 2000. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNQ59125.

The noble gas abundances and isotopic ratios of the terrestrial planets differ from each other and from the average of chondritic meteorites. These different abundance patterns result from primordial heterogeneities or different degassing histories. Magmatic transport is the only degassing mechanism that can be demonstrated to occur on Venus, Earth, and Mars, and is presently the dominant form of volatile transport to a planet's free surface. An alternative technique was developed to determine the partitioning and solubility of noble gases in mineral/melt systems. Natural end member minerals and synthetic melts known to be in equilibrium were held in separate crucibles in a one bar flowing noble gas atmosphere. Experiments were run 7-18 days at 1300 or 1332°C, in 99.95% Ar or a Ne-Ar-Kr-Xe mix. Gas concentrations were measured by mass spectrometry. The solubility of noble gases in minerals was surprisingly high, and individual samples of a particular mineral composition are distinct in their behavior. The data is consistent with lattice vacancy defect siting. Noble gas solubility in the minerals increases with increasing atomic number; this may be related to polarizability. Noble gas solubilities in melts decrease with increasing atomic number. Solubility is directly proportional to melt molar volume; values overlap the lower end of the range defined for natural basalts. The lower solubilities are related to the higher MgO and CaO concentrations and lower degree of polymerization and Fe³⁺ concentration in synthetic vs. natural melts. Partition coefficient patterns show a clear trend of increasing compatibility with increasing noble gas atomic number, but many individual values are > 1. Calculations show that the terrestrial planet atmospheres cannot have formed from partial melting of a common chondritic source. When results are examined with isotopic constraints and MOR and hot-spot activities, there is no compelling evidence that the Earth is substantially outgassed of its primordial or even its radiogenic volatiles. If volcanic degassing was mostly responsible for the atmospheres, then initial volatile abundances were Mars < Earth < Venus. Alternatively, roughly equal abundances could have been modified by catastrophic processes.

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Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Bibliography: leaves 126-128.

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The thesis is concerned with the derivation of anisotropic intermolecular potentials from experimental data. For the rare gas - hydrogen halide systems the most useful experimental results are those from molecular beam rotational spectra of van der Waals complexes and from pressure broadening of hydrogen halide rotational spectra by rare gases. Intermolecular potentials for the Ar.HCl system had previously been obtained from each of these experiments separately, but none of the potentials proposed succeeded in reproducing all the available data. In the present work, improved theoretical methods are developed for the calculation of molecular beam spectra and line broadening cross sections from a proposed intermolecular potential. The methods developed are substantially faster than those previously available, allowing their use in a least squares procedure to determine potential parameters. Several possible parameterisations of the intermolecular potential are then considered for Ar.HCl, and least squares fits of potential parameters to experimental results are performed for this system. Measurements of total differential cross sections and second virial coefficients are included in the least squares fits, in addition to the experiments mentioned above. The experimental data demonstrate conclusively that the equilibrium geometry of Ar.HCl is linear, with the atomic arrangement as written. The equilibrium intermolecular distance is 400±3 pm, with an absolute well depth of 18andpm;10 cm^-1 . The only feature of the potential which is not well determined by the experimental results is the behaviour around the linear Ar.Cl-H geometry. The results for Ar.HCl are then extended to the systems Ne.HCl, Kr.HCl and Xe.HCl, allowing the dependence of the intermolecular potential on the rare gas to be considered. The molecular beam spectra for Ne.HCl can be fitted only by a potential with a secondary minimum at the linear Ne.Cl-H geometry, in addition to the primary minimum at the linear Ne.H-Cl geometry. The experimental results for the other rare gas - HC1 systems are not very sensitive to this feature of the potential, and the potentials for these are constrained to be similar to that for Ne.HCl in this region. The potential surfaces for all the rare gas - HC1 systems have similar shapes, and appear to be nearly conformal. Finally, intermolecular potentials are obtained for the systems Ar.HF, Kr.HF and Xe.HF from molecular beam spectra. The experimental data for these systems are less extensive than for the HC1 systems, and the potentials obtained are reliable only in the region of the absolute minimum. The HF systems are considerably more anisotropic than the HC1 systems, and it is suggested that this is principally due to greater induction forces in the HF systems. Experiments are suggested which would provide further information on the intermolecular potentials for both HF and HC1 systems, and predictions of the results are made using the current best fit potentials.

Typescript (photocopy) / 167 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.) Dept. of Physics, University of Adelaide, 1978

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