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Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

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Song Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 50-54). / Abstracts in English and Chinese. / THESIS COMMITTEE --- p.ii / ABSTRACT --- p.iii / 中文摘要 --- p.v / ACKNOWLEDGENTS --- p.vi / TABLE OF CONTENTS --- p.vii / LIST OF FIGURES --- p.ix / LIST OF TABLES --- p.x / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter 1.1. --- Motivation --- p.1 / Chapter 1.2. --- Properties of Molecular Hydrogen --- p.3 / Chapter 1.3. --- Properties of Solid Hydrogen --- p.5 / Chapter CHAPTER 2 --- THEORY --- p.11 / Chapter 2.1. --- Group Theory --- p.12 / Chapter 2.2. --- Crystal Field Splitting --- p.18 / Chapter 2.3. --- Permanent Multipole Moment --- p.23 / Chapter 2.4. --- Predicted Rovibrational Spectrum --- p.26 / Chapter CHAPTER 3 --- APPLICATION: CARBON MONOXIDE IN SOLID PARAHYDROGEN --- p.28 / Chapter 3.1. --- Permanent Multipole Moment of CO --- p.28 / Chapter 3.2. --- Crystal field splitting --- p.33 / Chapter 3.3. --- Rovibrational Transitions and Relative Intensities --- p.42 / Chapter CHAPTER 4 --- DISCUSSION AND CONCLUSION --- p.46 / REFERENCE --- p.50

Semiclassical and Born-Oppenheimer approximations are used to provide uniform error bounds for the energies of diatomic molecules for bounded vibrational quantum number n and large angular momentum quantum number l. Specifically, results are given when (l + 1) < κ𝛜⁻³/². Explicit formulas for the approximate energies are also given. Numerical comparisons for the H+₂ and HD+ molecules are presented. / Ph. D.

<p> This thesis reports on the investigation of damage production in GaAs at low temperature using the channeling-backscattering technique.</p> <p> The study has been divided into two parts; first, the investigation of damage produced by 2 MeV helium ions in unimplanted and previously implanted samples with varied doses of 40 keV nitrogen and bismuth. The helium beam damage has been found to depend on the initial state of damage of the samples. In the second part the damage production due to 40 keV N+, As+, Sb+ and Bi+ ion implantation has been investigated. A comparison with damage production due to the corresponding 80 keV diatomic implants has also been carried out. No enhancement in the damage production was noticed due to the molecular implants.</p> / Thesis / Master of Engineering (MEngr)

<p> The frequency spectrum of a diatomic linear chain with randomly placed isotopic impurities is calculated using a Green's function formalism. The calculation follows a method devised by Langer, and yields the density of states exactly to first order in the concentration of impurities. It is found that polarisation mixing causes no problem and the results are analogous to those of Langer for the monatomic chain. Results are presented for various ratios of impurity mass to replaced mass, for which impurity bands are found above the optical band and in the gap between the accoustic and optical bands. A self consistent calculation is also discussed.</p> / Thesis / Master of Science (MSc)

Master of Science / Department of Physics / Carlos Trallero / Over the past four decades, the single-electron ionization of atoms has been a subject of great interest within the ultra-fast community. While contemporary atomic ionization models tend to agree well with experiment across a wide range of intensities (10[superscript]13-10[superscript]15 W/cm[superscript]2), analogous models for the ionization of molecules are currently lacking in accuracy. The deficiencies present in molecular ionization models constitute a formidable barrier for experimentalists, who wish to model the single-electron ionization dynamics of molecules in intense laser fields. The primary motivation for the work presented in this thesis is to provide a comprehensive data set which can be used to improve existing models for the strong-field ionization of molecules. Our approach is to simultaneously measure the singly-charged ion yield of a diatomic molecule paired with a noble gas atom, both having commensurate ionization potentials. These measurements are taken as a function of the laser intensity, typically spanning two orders of magnitude (10[superscript]13-10[superscript]15 W/cm[superscript]2). By taking the ratio of the molecular to atomic yields as a function of laser intensity, it is possible to "cancel out" systematic errors which are common to both species, e.g. from laser instability, or temperature fluctuations. This technique is very powerful in our ionization studies, as it alludes to the distinct mechanisms leading to the ionization of both molecular and atomic species at the same intensity which are not a function of the experimental conditions. By using the accurate treatments of atomic ionization in tandem with existing molecular ionization models as a benchmark, we can use our experimental ratios to modify existing molecular ionization theories. We hope that the data procured in this thesis will be used in the development of more accurate treatments describing the strong-field ionization of molecules.

The formidable progress achieved in the research at extreme conditions led to important discoveries of many unusual and interesting physical and chemical phenomena. Materials with high compressibility were and still are of particular interest due to a significant reduction of volume which could result in unexpected changes of bonding and/or electronic properties. Among highly compressible materials simple diatomic molecules such as H2, N2, and O2 are particularly interesting because they form new types of solids at high pressure. Hydrogen, being the most abundant element in the universe, possesses simple electronic structure, therefore, the study of hydrogen systems is of special interest. In the last three decades, there were subsequently explored and described several high-pressure phases of hydrogen up to 400 GPa. However, there is still a vast area of unexplained effects, which requires further analysis. The contributed work discusses Raman experiments in a wide pressure and temperature range where rotational and lattice phonon excitations have been measured in the Raman spectrum of solid H2 and D2 at 10, 77, 150 and 300 K from 2 to 180 GPa and up to 380 GPa at 300 K. Analysis of the Raman spectra allows to model how the rotational modes change with pressure and temperature and how the mass scaling laws evolve as the density increases in both hydrogen and deuterium. Comparison of vibrational frequencies of the isotopes appears to be extremely useful for estimation of equivalent pressures for both isotopes. Nitrogen and oxygen are archetypal elements possessing unique features such as extremely strong triple bond in case of N2 and magnetic moment in O2 . Both N2 and O2 exhibit rich polymorphism, with additional phases of O2 derived from its electronic and magnetic properties. N2 /O2 mixtures (for example, 20.9% O2 and 78% N2 mixture is air that we breathe) have been studied up to 12 GPa at 300 K experimentally and explored up to 500 GPa at 0 K theoretically. In the current project, N2 /O2 molecular systems are examined at 300 K up to 150 GPa. Rich polymorphism is observed, with seven phases exhibiting drastically different Raman spectra for concentrations below 45% of O2 and a more stable area with three phases in the concentration range from 45% to 80% of oxygen at pressures above 12 GPa. Moreover, characteristic Raman spectra obtained for the mix with 25% O2 after laser heating to approximately 2000 K at 25 and 96 GPa reveals pronounced peaks indicating the potential formation of new compounds.