Computer simulation by the molecular dynamic technique has been used to investigate the ionic crystal-water interface. The model consisted of a slab of sodium chloride in contact with water. The Born-Mayer-Huggins potential with the parameters found by Tosi and Fumi were used for the ion-ion interactions, water was modelled by the 'central-force potential' and the ion-water interaction by the potentials proposed by Heinzinger et al. The long range forces were evaluated by the Ewald method. We investigated (a) a system in which only the water molecules were allowed to move while the ions were fixed (b) a system in which all particles could move. Attention was focused on (a) on the behaviour of the water molecules near the crystal surface, and in (b) on the mechanism of the solution process.

Some properties of dislocations in aluminium and sodium chloride single crystals have been investigated by observing the generation of harmonics in an ultrasonic pulse travelling through a crystal. Pulses of 10 MHz longitudinal waves were generated at one end of a crystal with a quartz transducer and either 20 MHz or 30 MHz waves were detected at the opposite end of the crystal. The harmonic waves were detected either with a quartz transducer or a capacitative detector. Experiments on the generation of second harmonics due to dislocations were carried out on aluminium crystals. No dislocation contribution to the second harmonic was detected in NaCl crystals5 and this was attributed to a lack of purity in the crystals. However, experiments on third harmonic generation due to dislocations were performed on both aluminium and NaCl crystals. The amplitude of the third harmonics and the attenuation of the fundamental wave were measured as a function of impurity content, static bias stress, plastic deformation, temperature, the amplitude of the fundamental wave and, in the case of NaCl, X-irradiation also. The results of these experiments are compared with the behaviour predicted by the theory of Hikata and Elbaum (1966). Many of the results are found to be in good qualitative agreement with this theory. During the course of some third harmonic measurements in NaCl evidence was found of internal stresses remaining after plastic deformation. Compressive internal stresses were found after a plastic deformation in tension., and tensile internal stresses were found after further plastic deformation in compression. A previously unreported time dependence of the second harmonic and third harmonic amplitudes was noted in some crystals after a bias stress was applied. Thermal activation energies associated with the time dependent behaviour were measured. Such measurements provide a useful method of studying strain-ageing properties in crystals.

Far infrared absorption spectra (20-700cm-1) have been recorded using either a modified Grubb-Parsons/NPL cube interferometer with a maximum resolution of 0.1cm-1, or a Bruker 113V FTIR interferometer with a maximum resolution of 0.03cm-1, with samples mounted on a wheel inside a liquid helium cryostat close to the bolometer. Nominally pure GaAs and GaP samples and GaAs containing Al, B, C and Si impurities, were studied. The GaAs samples had either been irradiated with fast neutrons or 2MeV electrons with a range of doses varying from the minimum required to produce detectable changes in the infrared spectrum , up to a maximum corresponding to saturation of the damage produced. The only GaP sample to be studied was nominally pure and was irradiated with a dose of 2MeV electrons. All the samples were subsequently annealed in 30°C stages up to about 550°C at which temperature the recovery from the effects of theradiation damage was essentially complete and in many cases free carrier absorption had returned. The damage produced in the samples caused a relaxation of the selection rules, which normally forbid certain absorption processes, so that pronounced structure wasdetected which corresponded to features in the one-phonon density of states of the pure crystal. On annealing thesamples, the damage and hence this structure, was progressively removed. In addition, in GaAs irradiated with fast neutrons, new lines at 45cm 119cm-1 and328cm-1 were observed which first grew in strength withincreasing anneal temperature and then disappeared at higher temperatures. These lines were present in all samples given a sufficiently large dose of neutrons and hence were attributed to in-band resonances arising from intrinsic defect centres. However, in GaAs irradiated with 2MeV electrons only the feature at 45cm-l was observed, showing that the features at 119cm-l and 328cm-1 are produced only by neutron irradiation. In electron irradiated and annealed GaP a resonant mode at 149cm-1 was observed together with four gap mode lines which were all attributed to intrinsic radiation damage centres. In order to identify the defect centres responsible, these results were compared with a) the observations of local modes in doped samples which had undergone similar treatment and for which site switching of impurity atoms was observed during the annealing process and b) EPR data for similar annealing studies on the Asga antisite defect in irradiated GaAs. High resolution studies of neutron irradiated GaAs doped with carbon showed that the previously reported C(l) lines at 577.5cm-1 and 606cm-l show structure consistent with the centre responsible for these lines being Cas bonded to an interstitial As atom, surrounded by four Ga atoms.

The effects of quadrupolar interactions on the thermodynamics, statics and dynamics of linear molecules consisting of two Lennard-Jones centres is studied for the liquid phase. This is illustrated by using nitrogen, chlorine and carbon dioxide molecules as representative of the differing bond lengths that can arise in these systems. The changes due to the magnitude of the quadrupole moment are investigated for the chlorine system. Calculations of the structure of two-Lennard-Jones centre fluids is also carried out using the RISM method.

A comprehensive model of the excitation and kinematics of cometary molecules has been developed and used to analyze data obtained on comet Levy (1990c). This work builds on previous studies to develop models of the excitation and distribution of HCN and H$\sb2$CO in the coma and to apply these models to comet Levy in order to determine the physical parameters of the cometary coma and test models of the possible origin of H$\sb2$CO in comets. The collisional cross sections as a function of $\Delta$J have been considered in the excitation models for both molecules, based on quantum mechanical calculations. The vectorial model has been adopted for consideration of possible daughter species and a Monte Carlo calculation technique has been applied to develop both parent and daughter molecule models for H$\sb2$CO so that we can calculate its production rate and discuss its original source. With the high quality of spectra for both HCN and H$\sb2$CO molecules in comet Levy, we are able to use our models to constrain their abundance and some physical parameters of the coma. These new observational results confirm that microwave spectroscopy is an efficient tool to study cometary parent molecules, and help us understand the formation of our solar system.

Light actinides and copper systems were studied using resonant soft X-ray spectroscopy. An instrumental and experimental setup for soft X-ray spectroscopy meeting the requirements of a closed source for radioactivity was developed and described in detail. The setup was used for studies of single-crystal PuO2 oxidation. The existence of higher oxidation state than Pu(IV) in some surface areas of the single crystal were found from O 1s X-ray absorption measurements. Furthermore, from comparison with first principles calculations it was indicated that plutonium oxide with Pu fraction in a higher oxidation state than Pu(IV) consists of inequivalent sites with Pu(IV)O2 and Pu(V)O2 rather than a system where the Pu oxidation state is constantly fluctuating between Pu(IV) an Pu(V). It was shown that a combination of resonant O Kα X-ray emission and O 1s X-ray absorption spectroscopies can be used to study electron correlation effects in light-actinide dioxides. The electronic structure of copper systems was studied using resonant inelastic soft X-ray scattering and absorption spectroscopy. It was found that X-ray absorption can be used to monitor changes in the oxidation state but as differences between systems with the same oxidation state are in many cases small, speciation is uncertain. Therefore, a method utilizing resonant inelastic X-ray scattering as fingerprint to characterize complex copper systems was developed. The data recorded at certain excitation energies revealed unambiguous spectral fingerprints for different divalent copper systems. These specific spectral fingerprints were then used to study copper films exposed to different solutions. In particular, it was shown that resonant inelastic X-ray scattering can be used in situ to distinguish between CuO and Cu(OH)2, which is difficult with other techniques.

<p>Dissociative recombination (DR) is a process in which a positive molecular ion recombines with an electron and subsequently dissociates into neutral fragments. Among the different types of molecular ion-electron reactions DR deserves particular attention due to the important role it plays in low-temperature and low-density plasmas. Despite the apparent simplicity of the DR reaction, its investigation has proven to be a difficult task from both experimental and theoretical perspectives. In order to shed more light upon this process the storage ring technique has been introduced and utilised extensively for the last few decades. This thesis is devoted to experimental studies into the DR reaction at the storage ring CRYRING. The DR reaction has been investigated for the following molecular ions; Na⁺(D₂O), PD₂⁺, O₃⁺, N₃⁺, H₂⁺, D₂H⁺, OPCl⁺, OPCl₂⁺ and H₃O⁺, with the aim to ascertain rotational state effects, to find patterns in the branching products of similar molecular ions, to investigate isotope effects and to study in detail the dynamics involved in the three-body break-up channel.</p>

Dissociative recombination (DR) is a process in which a positive molecular ion recombines with an electron and subsequently dissociates into neutral fragments. Among the different types of molecular ion-electron reactions DR deserves particular attention due to the important role it plays in low-temperature and low-density plasmas. Despite the apparent simplicity of the DR reaction, its investigation has proven to be a difficult task from both experimental and theoretical perspectives. In order to shed more light upon this process the storage ring technique has been introduced and utilised extensively for the last few decades. This thesis is devoted to experimental studies into the DR reaction at the storage ring CRYRING. The DR reaction has been investigated for the following molecular ions; Na+(D2O), PD2+, O3+, N3+, H2+, D2H+, OPCl+, OPCl2+ and H3O+, with the aim to ascertain rotational state effects, to find patterns in the branching products of similar molecular ions, to investigate isotope effects and to study in detail the dynamics involved in the three-body break-up channel.

We have constructed a compact purely electrostatic ion-beam trap, ConeTrap, which we have mounted inside a double-walled vacuum chamber. In the inner vacuum chamber, we can obtain ultra-high vacuum (UHV) conditions and reach thermal equilibrium at well controlled temperatures down to 10 K. The chamber was constructed partly with the purpose of making high-precision measurements in ConeTrap, but also as a test-chamber for testing components (such as the detector-assembly tested and described in this thesis and paper III) to be used in the DESIREE (Double ElectroStatic Ion Ring ExpEriment) facility. The latter is a double electrostatic ion storage-ring being constructed at Stockholm University, in which the conditions are meant to mimic the environment in the interstellar medium. The interaction between two oppositely charged ions at very low relative velocities (controlled collision energies down to 10 meV) may then be studied in a section of the storage device where the two ion beams merge. The lifetime of loosely bound electronic systems, for example He-, is, at room temperature (and even at much lower temperatures), significantly affected by photons from blackbody radiation from the experimental device and its surroundings. The cryogenic temperature and low pressure obtained in the test chamber have made it possible to use ConeTrap to make the first correction-free lifetime measurement of the long-lived J=5/2 fine-structure level of the metastable 1s2s2p 4Po state of He-. Under the assumption of a statistical population of the fine-structure levels, at the time when the ions are created, we have also deduced the lifetimes of the short-lived J=1/2 and J=3/2 fine-structure levels. Furthermore, we have used ConeTrap to measure the pressure dependent storage lifetimes of He+ and Ar+ ions over wide ranges of temperatures and pressures, and we have thus been able to store positive ions with storage lifetimes of tens of seconds. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 1035. Adviser: Munir H. Nayfeh. Includes bibliographical references (leaves 100-104) Available on microfilm from Pro Quest Information and Learning.