No description available.

Molecular crystals are at the forefront of research to find new technologies and to probe emerging phenomena such as superconductivity. Their studies are, therefore, important but also challenging, especially in the field of atomically-resolved dynamics due to low damage thresholds and related factors. Two such crystals, showing different phenomena, were the focus of this work. The dynamics of photochemical reaction in ultrathin crystals of spirooxazines were studied using a home-built transient absorption setup and 266 nm light for excitation. They were found not to be completely photochromic in crystalline state, in contrast to their behaviour in solution and amorphous films. A transient emerges after excitation, which evolves to form planar trans-merocynanine product within 80 ps in solution, but due to steric restrictions in the crystal, only the ring-opened form of spirooxazine was created without undergoing isomerisation. For these experiments, a methodology was developed to tackle the issue relating to the permanent formation of the photoproducts in crystals, which severely hampers reversibility. It made use of an additional ultrashort beam, making it a three-beam approach, with the third beam acting to arrest the accumulation of the products by removing them from the probe volume via the back photoreaction. Using this approach, it was possible to achieve over 10,000 pump-probe cycles, enabling time-resolved spectroscopy of this system and opens up prospect for femtosecond diffraction experiments. Femtosecond electron diffraction study was carried out on EDO-MeEDO, a doped crystal of EDO-TTF. The response of the system was found to be different to what is known for the pure EDO-TTF crystal; our findings could not confirm the occurrence of a cell doubling phase transition. At acoustic time scales, it is hypothesised that cooperative effects play a role, which lead to pronounced phonon signals. Further studies are needed to understand the dynamics of this system.

No description available.

No description available.

High power RF deflecting cavities have found a wide range of applications which include particle separation, emittance exchange, X-ray pulse compression, temporal beam diagnostics, and crab crossing in colliders. However, conventional deflecting cavities suffer from beam degrading parasitic modes that are also confined within these cavities. Several mode damping/coupling schemes have been developed to solve this problem but they add to the cost, size, and complexity of the resonant cavities. Photonic Crystal (PC) accelerators and klystrons have benefited from the high mode selectivity of PCs where a specic EM state are confined to a defect in the PC while all other states are forced to propagate away. This work presents a systematic approach to designing a PC that confines only the TM110-like dipole Bloch state and forces the propagation of all other EM states. This dipole PC resonator was tuned and optimized for crabbing application at 11.9942 GHz (operational frequency of the crab cavity at CLIC). Also in this thesis, a carefully designed experimental measurement of the transmission spectrum of microwaves in a photonic crystal was used to demonstrate a well pronounced exhibition of the Dirac point in photonic analogues of graphene. This work adds to previous literature by studying the sensitivity of the Dirac point to the incident and receiving angles of waves propagating away from the Gamma - K direction at the input and output boundaries of the PC respectively. In addition, the challenges associated with the experimental retrieval of the dispersion plot of a photonic crystal were pointed out.

Research reported herein embraces two distinct aspects of vibrational spectroscopy. The first is that of VIBRATIONAL ANALYSIS. An introduction to the aims and methodology, and some of the problems and limitations of this discipline is provided. Results are reported for two systems, both complex and many-atom. Benzenetricarbonylchromium and its deuteriated analogue are investigated. The effects of ligation on the force constants of the benzene ring are evaluated and discussed; the normal modes are described; and the effects of kinematic coupling critically examined. An approximate vibrational model for CsNiC13 is presented, using a simple valence force field. Frequencies for both 'active' and 'inactive' modes are calculated, as are potential energy distributions and cartesian displacement coordinates. Parallel analyses are also presented for the related compounds CsNiF3, CsNiBr3, CSCoC13 and RbNiC13, and comparisons made. The second aspect is that of SINGLE-CRYSTAL VIBRATIONAL SPECTROSCOPY. An introduction is provided to the relevant theory and to various technical aspects, in particular infrared reflectance. Five compounds are examined. All the fundamental modes of tetragonal Pb0 are reported, and all but one assigned unequivocally by single-crystal techniques. The behaviour of the Eu reflectance band with decrease in temperature is thoroughly investigated and accounted for. Reflectance spectra are analysed and the relevant optical parameters computed. The first complete Raman spectrum, and single-crystal i.r. reflectance data are reported for orthorhombic Pb0, and an assignment proposed using a line-group approach. The unusual dielectric constant of the material is accounted for. Polarised single-crystal reflectance spectra are reported for methylammonium and propylammonium tetrachloromanganate (II) over the temperature range 295 to 50 K. Single-crystal Raman spectra over a similar range are also described. The main features of the spectra, particularly for the ambient temperature phases, are assigned with the aid of a factor group analysis. Single-crystal i.r. data for the planar molecule bis(dimethylglyoximato)nickel(II) are reported, and the out-of-plane skeletal modes located and assigned by direct experiment. Further necessary experimentation is detailed. Finally, accounts are provided of the computational methods used in the research, including a listing of a 'harmonic' oscillator programme developed by the author.

The crystal structure of 6-aminopenicillanic acid (C₈, H₁₂, N₂, O₃, S) (I) and cephalosporin Cc (C₁₄, H₁₇, O₆, N₃, S; CH₃CO₂H), (II) have been determined by X-ray crystallographic analysis. 6-aminopenicillanic acid crystallises in flat orthorhombic plates, Crystal data. a = 6.24 ± .02 Å, b = 14.83 ± .04 Å, c = 10.49 ± .03Å space group P2₁2₁2₁ Z=4. Using copper K_α radiation layers okl - 4kl and hkO to hk8 were recorded on equi-inclination Wissenberg photographs. A total of 988 reflections were measured visually out of a possible 1170 in the copper sphere. A Patterson function was calculated using data sharpened by the finction ¹⁄_f² exp.(3 Sin²θ), where f was the scattering factor for carbon; from this a superposition function was calculated. It was possible to obtain all atomic positions from this. These were refined using anistropic and isotropic least squares procedures, the final positions have calculated deviations of about .01Å. The final agreement factor was 11.6% using isotropic and 9.7%, anistropic temperature factors. The structure is similar to that reported by Crowfoot, Bunn, Rogers-Low and Turner-Jones for potassium benzyl penicillin except that in the thiazolidine ring the atom out of the plane of the other four is the nitrogen instead of the carbon to which the carboxyl group is attached, as in the other penicillins. The bond between the sulphur and the gem-dimethyl group is longer in all the penicillins than the generally accepted value for a C - S single bond (1.86 Å compared with 1.81 - 1.82 Å). The length of the C - N bond in the β-lactam group falls between that of a C - N single bond and that of an ordinary C - N peptide bond; this is probably caused by the lack of resonance in the fused β-lactam ring. Cephalosporin Cc crystalises in flat orthorhombic needles (a = 5.04 ± .0 Å, b = 7.00 ± .02 Å, c = 54.6 ± .2 Å), space group P2₁2₁2₁. 1521 Reflections out of a possible 2580 in the copper sphere were measured visually on equi-inclination Wissenberg films (layers okl - 3kl and hol - h51). The structure was determined and refined in a similar fashion to 6-aminopenicillanic acid, though because of the larger size of the molecule three rounds of Fourier refinement were needed before it was possible to use the least square procedure. The final agreement after eight rounds of least squares refinement was 10.6%, with calculated standard deviations of about .01 Å. The structure was identical to that proposed by Abraham and Newton. The bond distances were all within the expected range of values. The α-amino group of the side chain together with the acetic acid of crystallisation formed a hydrogen bond system around the screw axis parallel to b. There was no significant difference between the lengths bonds of the β-lactam group in cephalosporin Cc and in 6-aminopenicillanic acid.

In this thesis we consider two types of magnetic system, the ferromagnet and the antiferromagnet, containing substitutional impurities. The Heisenberg Hamiltonian is used and the spin-waves are examined by means of Green function equations of motion; the coherent potential approximation (CPA) is employed to obtain expressions for self-energies which are approximately valid for all impurity concentrations. In each case, an extension of the usual CPA is made: in Part I the impurities are described by scattering potentials with matrix elements on several lattice sites, and in Part II the effects of clusters of defects are included. In Part I, we discuss the dilute ferromagnet, and attempt to obtain an estimate of the critical concentration of magnetic ions by considering the long-wavelength spin-waves. The self-energy is calculated in such a way as to sum coherently the scattering of spin-waves from all sites affected by one impurity, although correlations between pairs of defects are neglected. We examine solutions for a single non-magnetic impurity and for small impurity concentrations; it emerges from these considerations that it is essential that the resonance which the non-magnetic ions produce at zero energy should be kept there by any approximation which is to be of use in describing the low-energy spin-waves. A generalized form of the CPA, suitable for extended defect matrices, is developed and used to derive expressions for the self-energy; detailed numerical results are presented. We find that although the CPA behaves well over most of the spin-wave band, it fails to describe the zero-energy resonance correctly, and this failure prevents us from deducing a value for the critical concentration. Two attempts to avoid this difficulty are described: the first uses defect Green functions to fix the energy of the resonance, the second moves it away from zero and outside the spin-wave band, but neither enables us to estimate the critical concentration. We also discuss a magnetic analogue of the percolation bond problem, to which the application of the CPA is successful. In Part II we apply the CPA to a calculation of the spin-wave energies in antiferromagnets containing either magnetic or non-magnetic impurities. Each site is allowed to have any possible number of impurities among its nearest neighbours; in order to deal with this we extend the CPA to deal with a large number of different defect types. Variations in the transverse interactions are not included in the CPA, but are treated in an approximate way afterwards. Expressions for the neutron scattering and Raman cross sections are derived in order to permit a detailed comparison of theory with experiment. The results of numerical calculations for three systems are presented: (Mn,Co)F₂, K(Mn,Co)F₃ and (Mn,Zn)F₂. These are compared with experimental data, and excellent agreement is found; in particular, the neutron scattering results agree extremely well, the line-shapes and widths being accurately described by the theory.

No description available.

The research in this thesis is centred on the design and development of novel coordination polymers (CPs) constructed from p-carboxylatocalix[4]arenes. Two design strategies were chosen as potential methods that would enable the rational design of CPs using transition metals (TMs) as directing centres and p-carboxylatocalix[4]arenes as building blocks. Each strategy was based on synthesising a target motif. The selection criteria for the target motifs were: 1) to provide the directionality in which the assembly could be extended and 2) be easily reproducible for a series of TMs. The first target motif is a planar binuclear metal cluster that can be extended in all three dimensions. The second motif is a TM complex containing a chelating ligand restricting the number of binding sites in the coordination sphere available to subsequent binding of ligands. In the preliminary study, using TM(II) ion (Co, Mn, Cd), mono-p-carboxylatocalix[4]arenes and bipyridines, a series of 1D CPs containing the target planar molecular panel were synthesised and characterised. The application of the "directional bonding" approach resulted in formation of the target second motif, a discrete coordination complexes constructed from TM(II) ion (Mn, Cd), mono-p-carboxylatocalix[4]arene and 1,10-phenanthroline. In the following study it was found that the steric effects of co-ligands used and the pre-organisation of the calixarene building block have a significant influence over the assembly process, dictating the topology of formed supramolecular architectures. Utilisation of the strategy based on the "directional bonding" approach, utilisation of a di-topic di-p-carboxylatocalix[4]arene resulted in formation of linear 1D CPs. Through exploitation of the di-O-alkoxycalix[4]arene C2 symmetry an alternative di-topic calixarenes were synthesised and used to construct spiral 1D CPs. It was also found that in certain reaction conditions these alternative di-p-carboxylatocalix[4]arenes assemble into discrete dimeric metal-organic calixarene capsules rather than spiral 1D CPs. In addition, it was demonstrated that di-p-carboxylatocalix[4]arene can also be used to synthesise 3D CPs.