There is paucity of data in the scientific literature pertaining to detailed assignments of the vibrational spectra of nitrogen containing thiocarbonyl compounds. Herein, three five membered heterocyclic compounds –rhodanine, 3-aminorhodanine, and 3-methylrodanine-containing both amide and thioamide moieties have been investigated from both an experimental and theoretical perspective. Experimental Raman (?o = 632.8 nm) and infrared spectra of the three compounds have been recorded in the solid state (protonated and deuteriated). Deuteriation studies revealed that not only are the protons attached to the nitrogen atom labile, but the protons of the active methylene group also undergo hydrogen-deuterium exchange. Comparisons of protonated and deuteriated spectra enable discrimination of the bands associated with N-H, NH2, CH2 and CH3 vibrations. Ab initio calculations, using density functional theory (DFT; B3-LYP) employing the cc-pVTZ basis set, have been conducted in order to obtain the geometry optimized, energy minimized structures of the isolated molecules in the gas phase. The data generated was then used to (a) compare, where possible, the calculated structure with the experimentally determined X-ray crystallographic structure, and (b) carry out normal coordinate analysis in order to obtain the potential energy distributions (PEDs) of each normal vibrational mode thus allowing detailed vibrational band assignments for the three molecules. The assignment of the bands associated with the amide and thioamide groups have been made possible by comparing the spectra of the three molecules and DFT calculations. In the case of rhodanine, the cis amide I mode is attributed to the bands at ~1713 and 1779 cm-1, whereas a band at ~1457 cm-1 is assigned to the amide II mode (Raman and IR). The vibrational bands for the thioamide II and III modes of rhodanine, 3-aminorhodanine, and 3-methylrhodanine are observed at 1176 and 1066/1078; 1126 and 1044; 1107 and 984 cm-1 in the Raman and 1187 and 1083; 1230 and 1074; 1116 and 983 cm-1 in the IR spectra, respectively. Surface enhanced Raman spectroscopy (SERS) studies of the three molecules have been conducted as a function of pH, concentration, and time in order to understand their interaction/absorption behaviour with citrate-reduced Ag and Au colloidal (substrate) nanoparticles, as well as for semi-quantitative trace analysis. The pH studies revealed that the optimum conditions for SERS analysis is the presence of HC1 and poly(L-lysine) at pH 2.3 (?o = 632.8 nm). The SERS studies also revealed the presence of a strong band at 1566/1575/1572 cm-1 (for rhodanine, 3-aminorhodanine and 3-methylrhodanine, respectively), irrespective of experimental conditions used.

Y2WO6: RE, Y2O2S: RE, Gd2O2S: RE phosphors have been prepared using the urea homogeneous precipitation method and firing. Stokes luminescence properties of Y2WO6: RE excited with a FRED (frequency doubled argon ion) UV laser (257 nm) have been studied. The emissions have been assigned to their corresponding energy levels. Differences in the emission spectra of Y2WO6: RE, Y2O2S: RE, Gd2O2S: RE and Y2O3: RE have been attributed to the different site symmetries of the rare earth ions and to the different phonon energies of the lattices. Fine nanostructures present within butterfly wing scales have been faithfully replicated using a precursor Y2O3: Eu phosphor solution. Monodisperse polystyrene spheres and SiO2 spheres were synthesised and they were used to synthesise well ordered bare opal templates. Photonic phosphor crystals of Y2O3: Eu, Tb, Gd and Y2O3: Tm were synthesised using these templates to study the photonic band gap properties. Nano-sized Y2O3: Eu phosphors have been successfully incorporated into mono-dispersed silica spheres which have been assembled into photonic crystals. It has been observed that when light-emitting phosphors (e.g. Y2O3: Eu) and dyes (e.g. acid red dye) are incorporated into the opal structures, their emission spectra are modified when the stopbands of the opals overlap the emission bands of the light-emitting materials.

Epitaxial growth of NiSb on GaAs(111)B substrates has been achieved for the first time. X-ray diffraction confirms the films are of high quality and oriented (0001) with respect to the (111) substrate. Surface reconstructions have been observed on NiSb thin films through electron diffraction performed in situ during and after growth. Three different surface reconstructions have so far been observed. Two of these, the (4×4) and (4×6) reconstructions, are entirely new to the binary pnictides. The latter, however, is only metastable. The third reconstruction is a td(1×3) and is believed to be related to similar reconstructions seen on MnSb and MnAs. The epitaxial growth of MnSb on GaAs(111)B substrates has been the subject of a J dependent growth study. It is seen that the final surface morphology is highly sensitive to the local beam flux ratio, J, with changes of a few percent leading to sharp and abrupt changes in the morphology. An XRD investigation of these films reveal varied and complex behaviour, with the appearance of a large number of reflections which do not originate from either GaAs(111) or MnSb(0001). Cubic MnSb(111) crystallites have been seen in some thin films in a variety of strain states with evidence of tetragonal distortions. Surface preparation methods of air-exposed MnSb has been investigated using a combination of x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and x-ray mangetic circular dichroism (XMCD). A thick Mn-oxide layer, which is resistant to conventional in situ ion-bombarding and annealing (IBA) methods, is formed after exposure to air. Such surfaces are found to be non-magnetic. A simple combination of HCl acid etching followed by in situ IBA treatments is found to result in a well ordered (2×2) surface, with the recovery of a magnetic surface. A new antimony capping procedure has been investigated and found to be effective in preventing oxidation of the surface even after prolonged exposure to air. Such samples are found to retain a magnetic surface. It will also be shown that detailed analysis of the XMCD is not possible due to jj coupling which precludes the use of the sum rules, whilst theoretical calculations within the SPR-KKR DFT framework fail to adequately describe some aspects of the bulk magnetic behaviour. Quantitative surface structure determination using co-axial impact collision scattering spectroscopy (CAICISS) and low energy electron diffraction (LEED I-V) has been performed on the MnSb(0001)-(2×2) reconstruction. In total, 68 unique surface structures have been trialled, with none of them fitting the experimental data to any degree of satisfaction. A number of key observations have however still been made. Firstly, the LEED I-V suggests the MnSb is bulk-terminated with antimony and consists of a manganese-rich surface layer. This agrees with RHEED observations made during and after growth. However, both the CAICISS and LEED I-V data show the surface region to be six-fold symmetric, in direct contradiction with the bulk symmetry. In addition, the CAICISS data indicates the bulk structure is not preserved all the way to the surface, with the Sb–Sb and Mn–Mn layer separations being approximately equal. This suggests the structure of the outermost MnSb layers deviate significantly from the bulk structure and has profound implications for the surface magnetic and electronic properties, as well as for epitaxial growth with MnSb acting as the substrate.

This thesis presents a new family of single-determinantal ab initio electronic structure models ideal for the black-box computational investigation of molecular phenomena. These theories mimic Variational Coupled Cluster and achieve an approximately fulfilled variational upper bound property on the exact ground-state Schrodinger energy eigenvalue, while not exceeding the limiting computational complexity of the well-known CCSD method, and without sacrificing any other advantageous methodological property. In particular, these Approximate Vari- ational Coupled Cluster Theories are formulated through the minimization of a rigorously extensive and orbitally-invariant functional that treats certain limiting systems exactly. Unlike CCSD and related methods, for which it is extremely problematic, these theories are highly robust to the breakdown of the Hartree- Fock approximation that occurs when the single Slater determinant of minimal energy becomes an inadequate qualitative description of the true electronic wavefunction. Furthermore, presented results suggest that when the essential physics of strong non-dynamic correlation is captured by a near-variational ansatz, remaining dynamic correlation effects may be legitimately included perturbatively, with implications for the design of future electronic structure models because the failure of methods such as CCSD(T) to describe the dissociation of multiple bonds may be ascribed to the inadequate non-variational description of the electronic structure at the CCSD level, and not to a breakdown of perturbation theory; Optimized-Orbital Quasi-Variational Coupled Cluster Doubles with a perturbative treatment of triple excitations (OQVCCD(T)) is capable of predicting a physically correct and quantitatively accurate potential energy curve for diatomic nitrogen, N2, which has not been achieved, at the time of writing, by any other practical (O(o2v4)-iterative O(o3v4)-non-iterative) method based on Restricted Hartree-Fock theory. The method is demonstrated to be additionally suitable for the black-box description of singlet multiradicals through application to model hydrogen chains.

We discuss existing free energy methods for use with investigation of solid-solid polymorphism. An alternative implementation for phase switch Monte Carlo is introduced which samples from two synchronised Markov chains exploring both polymorphs, using a set of generalised coordinates to transform between Markov chains. This is validated against the existing results for face-centred cubic (fcc) and hexagonal close-packed (hcp) hard sphere crystals. The extension to more complex crystals including flexibility and constraints is explored. This extension is applied to a hard sphere model of linear alkanes. A phase transition in density is accurately located between two polymorphs of n-butane with increasing density; this is suggested as a rigorous benchmark for free energy methods. We also demonstrate the importance of including anisotropic volume moves when simulating crystalline solids. Generalised coordinates for any fully flexible molecular system of soft particles are presented. These are used to investigate a coarse-grain model of cholesterol in regards to the polymorphic transition between two anhydrous cholesterol crystals. A phase transition in temperature is found and the limitations in the model are discussed.

This thesis concerns molecules with potential uses for information storage on the atomic scale. Density functional theory (DFT) calculations are used to study the molecules in depth, to further understand their properties and to ascertain whether they are suited to such applications. Throughout this thesis, particular attention is paid to the effect of the surface on the properties of the adsorbates. This includes the effect of dispersion interactions, the quenching effect of a metal surface on the spin moment of the adsorbate and the role of a polarising thin film in stabilising various charge states of a molecule. The molecule 4-carboxy-TEMPO (4CT) is studied, adsorbed on Cu(110). In gas-phase, this molecule has an unpaired electron on the NO group, surrounded by methyl groups which could shield the radical from being quenched when adsorbed on a metal surface. Spin-polarised DFT calculations are used in combination with scanning tunnelling microscopy simulations to identify the adsorption geometry of 4CT on Cu(110). Information about the electronic structure of the system from the DFT calculations is then used to determine that the NO radical is not preserved upon adsorption on Cu(110). Following this, DFT calculations of cobalt tetraphenylporphyrin (CoTPP), also adsorbed on Cu(110), are used to examine the magnetic properties of the system. Specifically, whether the spin moment of the central Co atom is quenched upon adsorption on the metal. The treatment of the highly-correlated d-electrons of the Co atom is problematic for semi-local DFT, such as GGA. As a result, the impact of the inclusion of an on-site Coulomb repulsion, U , is studied to understand its effect on the spin moment of the Co. Methods for the self-consistent calculation of U are assessed and ivcomparisons are made with experimental measurements of the spin moment of the Co by X-ray magnetic circular dichroism (XMCD). An overestimation of the value of U by self-consistent methods is discovered, which leads to qualitatively wrong magnetic behaviour, however, it is found that the experimentally observed moment is observed for calculations carried out for a narrow range of U -values. The copper complex, bis-dibenzoylmethanato-copper (Cu(dbm) 2 ), is next to be studied. Experimental work on this complex showed that, upon being exposed to an STM voltage pulse, it exhibited a reversible switching behaviour when adsorbed on a NaCl bilayer on Cu(111) and Cu(100). By using a recently developed perfect conductor (PC) model, where the metal substrate is replaced by a PC, calculations of the oxidation and reduction of this system can be carried out. Such calculations reveal that the ionic polarisation of the NaCl thin-film is able to stabilise various charge-states of the complex. Furthermore, it is shown that charging of the complex is not sufficient to explain the switching, with a new charged state being found to be necessary to explain the switching process. This new charge state, predicted by the theoretical calculations, was later observed experimentally. Finally, a study of the hydrogen transfer in porphycene (Pc) on Cu(110) is conducted. A nudged elastic band calculation is used to determine the minimum energy path and barrier height of hydrogen transfer in this molecule, showing that the transfer proceeds step-wise through a short lived trans state, and not via concerted motion of the hydrogens. By calculation of the frequencies of the N-H modes of the adsorbed molecule it is shown that the zero point energy of the hydrogens has a significant role in lowering the barrier of the transfer process. These results show the important part played by the surface in the behaviour of the adsorbates, and illustrate how interaction with a surface can qualitatively alter the behaviour of adsorbates in comparison to the gas-phase. Theory and experiment are brought into contact and used to both refine theoretical understanding, and to direct further experimental studies.

The photodegradation of the selected steroid hormones, 17β-Estradiol (17β-E2), 17α-Estradiol (17α-E2), Estrone (E1) and Progesterone (PG) in aqueous solutions has been studied using the Downflow Gas Contactor Reactor (DGCR). The performance evaluation of the DGCR as providing an efficient and economical advanced oxidation process (AOP) demonstrated that it can be considered a promising AOP capable of total degradation in a short period of time. A fast and reliable chromatographic method was developed and validated to study the performance of the DGCR down to the ng L–\(^1\) level. Hydrodynamic and mass transfer characteristics of the DGCR were examined extensively, and the optimum operating conditions were identified. The photodegradation process fit well with pseudo-first order kinetics with R\(^2\) ≥ 99%. UV irradiation is the main factor affecting the whole degradation process. The effect of the initial concentration, initial pH, different O2 flowrates, hydrogen peroxide and different combinations of UV systems with the DGCR were all explored to evaluate the photodegradation performance and the removal efficiency. These results show great promise for the DGCR that it can be considered a promising AOP at the industrial scale applications.

The history of the development of the understanding of the statistical arrangement of hydrogen bonds in ice Ih and the discovery of the transition at 72 K to the ordered phase, ice XI, catalysed by alkali hydroxide doping, is reviewed. Possible ordered arrangements of hydrogen bonds are discussed and enumerated. A theory is presented relating the entropy and permittivity of partially ordered ice to the degree of order. The apparatus developed for dielectric experiments on KOH-doped ice is described. The results of such measurements for polycrystalline specimens and one single crystal are presented. Measurements above the transition reveal that the main charge carriers are OH\(^-\) ions, with a temperature-independent mobility of approximately 10\(^-\)\(^1\)\(^0\) m\(^2\) v\(^-\)\(^1\) s\(^-\)\(^1\). The transformation to the ordered phase starts when the sample is cooled below about 65 K, and once started can be speeded up by heating the sample to 67-70 K: the static permittivity and the a.c. conductivity slowly decrease. Neutron powder diffraction experiments were performed on HRDP at ISIS. After one unsuccessful experiment, dielectric measurements on powder samples showed the importance of excluding CO\(_2\) during preparation. In a second experiment the structure of ice XI was confirmed and the lattice parameters determined for the first time.

The aim of the project described in this thesis was to develop a system in house that would be capable of providing a technique to enhance the reliability of detection of threat agents such as compounds used for chemical warfare and explosives. This was to be done by using a combination of an ion mobility spectrometer (IMS) in tandem with a quadrupole mass spectrometer (QMS). When meeting these requirements, the latest electronics and software were incorporated in the instrumentation to maximise sensitivity and flexibility. By attaching a QMS to an IMS, an extra dimension in specificity is gained whereby a more positive identification of a compound is made based on m/z values, thereby providing further information on the ion-molecule processes taking place in the IMS. Flexibility in operation was achieved by using the graphical programming language LabVIEW for the software aspects, allowing program development and modification to be made more quickly than would be the case than if a procedural language such as C++ had been used. A special ‘pulse to analogue’ converter developed during the project provided increased sensitivity and resolution over earlier systems in regard to obtaining selected mass mobility spectra. Proof-of-principle measurements are provided that demonstrate the capabilities of the newly developed IMS-QMS system in both positive and negative ion modes of operation, with some results obtained that are consistent with those from previous investigations. Data obtained for various chemicals not previously investigated are also provided.

Metal hydride materials have attracted much interest for their potential use as hydrogen storage materials. Complex hydrides are amongst the most promising due to their high gravimetric storage capacities and favourable de/rehydrogenation conditions. Here, mixed anion complex hydrides are investigated both through halide doping of LiNH\(_2\) and Li\(_2\)NH, and though a mixed LiNH\(_2\)-LiBH\(_4\) system. The reaction of LiNH\(_2\) and Li\(_2\)NH with lithium or magnesium chloride, bromide and iodide has been shown to form a series of amide- and imide-halide phases. The structures of these phases were investigated through powder diffraction methods as well as Raman spectroscopy. The hydrogen releasing properties of these materials were investigated through reaction with LiH and MgH\(_2\); while the equivalent hydrogenation reactions were also tested. In both cases these materials performed more favourably than the pure LiNH\(_2\)-LiH system. The lithium ion conductivity of these materials was also investigated; it was shown that the most conducting materials were also the quickest to release and uptake hydrogen. The LiNH\(_2\)-LiBH\(_4\) system was studied, with particular focus on the decomposition product, Li\(_3\)BN\(_2\). All three known polymorphs of this compound were shown to be able to form by the reaction of \(_2\)LiNH\(_2\) + LiBH\(_4\) by carefully changing the reaction conditions. Further stages of this system were investigated through reaction of Li\(_2\)NH and Li\(_3\)N with LiBH\(_4\). Here the products from these reactions were studied along with the thermal desorption properties of the systems.