Thesis Work/Research
Examinator: Prof.Thomas Nortons
Supervisor:Dr.Chung
During my research under the supervision of Dr. Chung carried out theoretical studies for atomic systems containing several electrons. Atomic properties such as energies, wave functions, lifetimes, isotope shifts, fine and hyperfine structures are calculated for bound states as well as highly-excited resonance systems. Polarizability and dynamic polarizability of atomic systems are also computed to obtain the van der Waals coefficients for molecules. New methods, such as saddle- point techniques, full-core plus correlation, and restricted-variation methods are being developed in order to overcome the difficulties encountered in other theoretical approaches. These methods have been highly successful; very high precision results are obtained for three- and four-electron systems.
The results thus obtained are very useful to experimentalists in the analyses of observed optical and electron spectra. Calculations are underway to apply these methods to five- and six-electron systems.
Dr. Mowat does experiments to measure the ways that simple molecular ions neutralize by recombining with free electrons. The reaction rate for recombination is an important quantity that, for example, effects chemo-synthesis in interstellar clouds. The ions are confined in a storage ring. The storage ring is a large, yet very sensitive, accelerator-like instrument in which the molecular ions continuously circulate at very high speed in an extremely high vacuum. The ions all have nearly the same kinetic energy.
My research group combines diffuse X-ray scattering methods with computer simulation and optical diffraction modelling to deduce the arrangements of atoms and molecules in disordered crystals. Conventional crystal structure determination reveals only averaged arrangements, inadequate to explain some of the basic properties of the many minerals, inorganic compounds, organic compounds and alloys which exhibit crystalline disorder. Diffuse scattering gives information on how neighbouring atoms or molecules interact with each other. Quantitative studies of diffuse scattering are, however, still rare because of the intrinsically very low intensities involved.
The Disordered Materials Group had developed a dedicated diffuse-scattering diffractometer system based on the Stoe curved position-sensitive wire detector (PSD). This allows high quality diffuse scattering data to be efficiently recorded over large volumes of diffraction space and provides a unique facility for tackling a whole range of problems not previously feasible. A second instrument has now been constructed, which, as well as providing additional data collecting capability,allows measurements to be made with Mo-Kalpha radiation and is suited to a range of materials that were too highly absorbing for investigation on the original system which used CuKalpha radiation only.
The group's interests span a wide range of different fields, each presenting problems for which this specialised technique can give unique information.
Dr Thomas research information have more about the diffuse scattering including his own work and papers in this field.
Disordered molecular crystals including ones having e.g. anomalous optical properties. Here the aim is to understand the basic interactions between molecules, how these give rise to the particular state of order and the relationship of this to the physical properties of the materials.
Non-stoichiometric inorganic materials typified, e.g. by the cubic stabilised zirconias and mullite which is a major component of all aluminosilicate ceramics. these both have commercially important properties which are intimately associated with their atomic ordering patterns. Wüstite is another material in the category which is important because it is thought to be a major constituent of the earth's lower mantle. Any description of the structure of these materials which does not account for the complex diffuse diffraction patterns they exhibit, cannot hope to satisfactorily explain their properties and behaviour.
Flexible open-framework structures such as SiO2 silica polymorphs cristabolite and tridymite and their analogues. Also included in this category are guest-hosts systems such as urea inclusion compounds and zeolites, which are important catalytic materials.
Quasi-crystal phases which have been found in a large number of alloy systems since the original discovery in 1984, have attracted the group's attention recently, not only because they present fundamentally new concepts, but also because it is clear that in many cases disorder is an important aspect of the problem.
