No description available.

The first part of this thesis gives a general introduction to theoretical and practical considerations in the application of infrared spectroscopy to analytical problems. Part 2 gives the results of several investigations made with the aid of vapour-phase infrared methods. Following (a) a brief description of the general experimental procedure, sections describe the results obtained in investigations of (b) the behaviour of thioalkyl compounds under Zeisel reaction conditions (c) the behaviour of propoxyl and butoxyl groups in the Zeisel reaction (d) the Zeisel determination of tert-butyl groups and the anomalous reaction of tert-butyl phenols (e) the determination of small amounts of alcohols in aqueous solution (f) anomalous results arising from cleavage by hydriodic acid (g) the determination of 1,2-diols by a modified Zeisel reaction (h) simultaneous determination of uronic acid and alkoxyl groups in polysaccharides by reflux with hydriodic acid. Part 3 presents the results of a study of the infrared spectra of some carbohydrates in aqueous solution. Several figures indicate the type of spectra which can be obtained. In general the differences between the spectra of simple sugars are not sufficiently distinctive to facilitate the analysis of unknown mixtures of several sugars such as commonly occur in studies of natural products. Part 4 presents a comparison of the results obtainable for the analysis of some of the inorganic components of the ash obtained from natural carbohydrate materials such as plant gums. The methods used included x-ray fluorescence, flame photometry and chemical analysis using ethylene diamine tetraacetate. Comparisons of the results obtained are presented and the advantages and limitations of the methods are discussed.

Chapter 1 gives an introduction to hydrogen bonding and the existing research surrounding short strong hydrogen bonds. The concept of a reversible, temperature dependent, proton migration is introduced and a selection of systems in which this proton migration has been observed to date is discussed. Chapter 2 describes the synthetic techniques, characterisation methods and computational procedures used throughout this work. Chapter 3 describes the variable temperature structural studies on 3,5 pyridinedicarboxylic acid and its deuterated analogues. The fully deuterated analogue undergoes a non-classical, first order, isosymmetric phase transition between 150 and 200 K and DFT calculations have identified vibrational free energy changes as the driving force for this. Although similar behaviour is exhibited by two partially deuterated isotopologues, no such transition is observed in the fully protonated form. Chapter 4 presents a combined spectroscopic and computational study of three isotopologues of 3,5-pyridinedicarboxylic acid. Whilst spectral observations and diffraction data are coincident for the fully deuterated form, the advantage of spectroscopy over diffraction for describing migration in the fully protonated and a partially deuterated isotopologue is demonstrated. Chapter 5 explores the role of vibrational coordinates in the PES governing proton dynamics in light of NMR relaxometry measurements, which reveal a non zero dynamical rate at temperatures close to 0 K, indicative of proton tunnelling. Tunnelling is confirmed by the presence of a 2-well potential in the system, and described based on reorganisations within the structure as a whole. Chapter 6 reports the synthesis of further short strong hydrogen bond systems. The variable temperature structural properties for each of these compounds are discussed, and comparisons with other well known proton migration compounds are drawn. Chapter 7 presents the attempted synthesis of a series of new co-crystals, with components based on those of 4-methylpyridine-pentachlorophenol; the successful products were found to possess medium length hydrogen bonds. Variable temperature diffraction studies for one of these products are discussed and show that it undergoes a phase transition on cooling resulting from slight rotations of its components. Chapter 8 gives the main conclusions of this thesis and outlines a number of opportunities for further work.

No description available.

Femtosecond time resolved photoelectron imaging spectroscopy equipment was designed, constructed, and used to reveal the non-adiabatic dynamics of model biological systems. Indole and phenol derivatives were studied as models for eumelanin, a pigment found in humans designed to protect the body from ultraviolet radiation. The photo-dynamics of these molecules was studied after excitation with ultraviolet radiation, with particular emphasis on the effect that the hydroxyl groups have on the p * dissociative state. It was found that adding a hydroxyl group onto indole to create 5-hydroxyindole had little significant effect on the photodynamics at the excitation wavelengths studied. Adding a second hydroxyl group to phenol had a strongly marked effect only when the hydroxyl groups were in close proximity to each other, in which case it dramatically increased the relaxation rate. An ultrafast optical system, imaging photoelectron spectrometer, and software to control the hardware, and collect and analyse photoelectron data were successfully implemented and used to collect and analyse data. This system will be of use for many more years and will be the basis of much future research.

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The ring-disc electrode consists of a central disc electrode which has an insulating annulus around it, forming the gap, and this in turn is surrounded by a ring electrode. The usefulness of this system lies in the fact that a reactant can be generated on the disc, and then it can be monitored at the ring as it is transported outwards by radial convection and diffusion. The first chapter of this thesis discusses the importance of the ring-disc electrode and reviews its development and application to the study of electrode processes, to solution kinetics, and to analytical problems. Most of the work prior to 1966 was of a qualitative or semi-quantitative nature owing to the lack of exact solutions to the problem of the transport of a species from the disc to the ring. This was largely resolved by the publication of a series of papers by Albery and Bruckenstein (1), who presented a new approach to the theory and in particular obtained solutions for cases where the intermediate is consumed by first- or by second-order kinetics. The work described in this thesis has been directed towards testing and applying these theories. Experiments with the ring-disc electrode usually involve the simultaneous and independent measurement of the ring electrode and disc electrode currents, while maintaining the potential of one electrode constant with respect to a reference potential. This is most readily achieved by the use of operational amplifiers, and Chapter 2 of this thesis describes the design, construction and use of a multi-purpose, operational amplifier, electrochemical control unit; experiments on the amplifiers used in the unit were carried out to test their suitability for use in D.C. electrochemical control circuits and this is dealt with in an Appendix to the thesis. The other apparatus used throughout this work together with other essential experimental details are dealt with in the third chapter. A fundamental parameter for the ring-disc electrode is the collection efficiency, N. This is a function only of electrode geometry and the theoretical value is obtained by calculating the limiting ring current for a given disc current; a resumandeacute; of this theory is contained in Chapter 4. The final chapter of the thesis discusses the range of first- and second-order rate constants measurable with the ring- disc electrode, the various advantages and disadvantages of the technique and possible future applications to homogeneous kinetic studies.

The ultra-violet and X-ray photoelectron spectra of the tris-hexafluoroacetylacetonato complexes of cone transition metals are reported and discussed. For many of these complexes there is either little or no literature experimental data available and, where necessary full details have been given in this thesis, both of the preparation and purification of the complexes. The gas-phase ultra-violet photoelectron spectra are discussed first, and it is shown how the spectra lead unambiguously to an energy level ordering similar to that assumed in ligand-field theory. However, in the high-spin complexes of Mn(III) and Fe(III) and in the low-spin Co(III) complex, the metal levels are observed to have ionisation energies which, for the most part, are higher than those of the least stable ligand molecular orbitals. This is in direct contradiction to the predictions of ligand-field theory and, in the case of the Co(III) complex, leads to an inversion of the trigonally split e and a₁, metal d orbitals. The interpretation of the high-spin complex spectra is shown to be very difficult within the one-electron framework used for the other complexes and the ultra-violet spectra are shown to be the best guide to interpretation. The values for the ligand-field parameters so derived are similar to, though slightly larger than, those for the neutral species. The ESCA spectra of the complexes were measured and are reported in the second part of the thesis. The movements of the core levels so found are related by an expression derived by Siegbahn et al. to the charge shifts in the complexes as the metal is changed. These charge shifts are of three basic types: a polarisation of the andpi; framework of the ligand towards the metal as the metal-oxygen bond length contracts, a transfer of charge from the ligand andsigma;-system to the metal, increasing as the transition series is traversed and a charge shift from the anti-bonding metal d-orbitals back onto the andsigma;-system of the ligand as a natural consequence of its anti-bonding character. As a parallel study, the ESCA spectra of the metallocenes were also run and are reported at the end of the second part of the thesis. The charge shifts observed in these compounds show a remarkable parallel to those found in the hexafluoroacetylacetonato complexes, when the different metal charges and ligand characteristics are taken into account. These trends were shown to be in accord with other data on the metallocenes. In the last part of the thesis, the charge and orbital energy shifts deduced in the first two parts of the thesis for the hexafluoroacetylacetonato complexes are correlated with other physical measurements and a consistent picture of the bonding in these complexes shown to emerge. In particular, the shifts in ionisation energies found for many of the main bands in the ultra-violet photoelectron spectra receive a ready explanation once the ESCA data is considered. On this basis a case is made for the complementarity of the two techniques.

No description available.

La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) is an oxygen ion conducting electrolyte material widely used in solid oxide fuel cells (SOFC). La2NiO4+δ (LNO) is a mixed ionic-electronic conducting layered perovskite with K2NiF4 type structure which conducts oxygen ions via oxygen interstitials. LNO has shown promising results as an SOFC electrode in the literature. In this work the compatibility and performance of LNO electrodes on the LSGM electrolyte material for solid oxide electrolysis cell (SOEC) is investigated. The materials were characterised as SOEC/SOFC cells by symmetrical and three electrode electrochemical measurements using Electrochemical Impedance Spectroscopy (EIS). Conductivity and ASR values were obtained in the temperature range 300-800°C with varying atmospheres of pH2O and pO2. The cells were also subjected to varied potential bias, mimicking fuel cell or electrolysis use. Enhancement of LNO performance was observed with the application of potential bias in both anodic and cathodic mode of operation in all atmospheres with the exception of cathodic bias in pO2 = 6.5x10-3 atm. In ambient air at 800°C LNO ASRs were 2.82Ω.cm2, 1.83Ω.cm2 and 1.37Ω.cm2 in OCV, +1000mV bias and -1000mV bias respectively. In low pO2 at 800°C LNO ASRs were 9.17Ω.cm2, 1.74Ω.cm2 and 456.9Ω.cm2 in OCV, +1000mV bias and -1000mV bias respectively. The increase in ASR with negative potential bias in low pO2 is believed to be caused by an increase in mass transport and charge transfer impedance responses. Material stability was confirmed using X-Ray Diffraction (XRD), in-situ high temperature pH2O and pO2 XRD. In-situ XRD displayed single phase materials with no observable reactivity in the conditions tested. Scanning Electron Microscopy images of cells tested by EIS in all atmospheres displayed no microstructure degradation except for those cells tested in a humid atmosphere which display a regular pattern of degradation on the LNO surface attributed to reaction with the Pt mesh current collector.