The structures of molten ZnCl2, ZnBr2 and ZnI2 have been determined by pulsed neutron diffraction. A tetrahedral configuration of anions around each cation was found for all three salts, which was extremely well defined for ZnCl2 and ZnBr2. Intermediate range ordering was also observed for all three salts and was seen to increase through the series from ZnCl2 to ZnI2. These observations are discussed with reference to previous studies of molten 2:1 salts, ion polarization effects and directional dependence of interionic forces. The effect of temperature upon the structure of molten ZnCl2 has also been investigated. In addition to this study of pure molten salts, the effect of structural modification of the 'network liquid' ZnCl2 by the addition of 'structure breaking' KCl has been studied. Pulsed neutron diffraction patterns were obtained from molten mixtures across the composition range. Upon addition of KCl, the local tetrahedral structure around each zinc ion was found to be very stable, even up to high KCl concentrations, and the intermediate range ordering in ZnCl2 not only persists, but was seen to increase, and to still be present even at 81% KCl concentration. Possible explanations of this behaviour are discussed and suggestions for further work are made. The structural modification of molten nickel halides by the addition of nickel metal has also been studied. A solution of NiI2 + 9 molar% Ni has been investigated by pulsed neutron diffraction from two isotopically enriched samples, and a solution of NiBr2 + 9 molar% Ni has been investigated by steady-state neutron diffraction from three isotopic samples. There was no evidence for subhalide complex ion formation involving more than one metal atom. The results suggest that nickel is ionising according to the equation Ni ? Ni2+ + 2e, with nickel ions occupying existing sites within the liquid structure and electrons acting so as to screen the interionic potentials. The maximum entropy method has been discussed and applied to the problem of structure factor data analysis. This method proved to be useful in the interpretation of some of the data presented in this thesis.

The preparation of the adducts formed between antimony pentafluoride and the oxide tetrafluorides of uranium, molybdenum, tungsten and rhenium is described. Structural details from full single crystal X-ray investigations are reported for the adducts UF4O. 2SbF5 and MF4O.SbF5 (M = Mo or Re). The rhenium adduct forms discrete fluorine bridged rings of the dimer 2(ReF40.SbF5), the molybdenum adduct has a polymeric zig-zag chain arrangement, and the UF4O. 2SbF5 structure contains both the ring and chain units in a three-dimensional network. Crystallographic and vibrational spectroscopic evidence indicate a small ionic contribution in the bridging bonds. The structures of three complex fluorides of the form A1BVF6, previously studied by X-ray powder diffraction, have been redetermined. NaTaF6 and a new triclinic form of (?-) CsNbF6 were studied by X-ray single crystal methods, and NaWf6, by refinement of data from neutron diffraction of the microcrystalline powder. The NaTaF6 structure is found to be consistent with the previously described face centred cubic (NaSbF6) type, however, the NaWF6 structure has been reassigned as primitive cubic (Pa3). Structures of two complex Quorides of the A12BivF6 general form are reported. (NH4)2PtF6 was found to be of the face centred cubic (K2SiF6) type and K2OsF6 of the trigonal (K2GeF6) type. Three structures are described that are considered as incomplete due to unsatisfactory refinement of the fluorine atom positions in apparently disordered structures. For NF4.SbF6, difficulty was encountered in the refinement of fluorine atom positional parameters about the antimony atom. Similar problems were encountered in the location of the fluorine atoms of the hydroxonium salts H3O.MF6 (M=Sb or Ta). Finally the preparation and crystal structure of WF5N3, the first azide derivative of a transition metal fluoride are reported. Unsuccessful attempts to isolate M0F5N3 and WF6-n(N3)n (n>2) are also described.

The spectroscopy and pyrolysis of a number of group III organometal- lic compounds used for the growth of semiconductors by Metal Organic Vapour-Phase Epitaxy (MOVPE) have been investigated using Fourier transform infrared spectroscopy and Infrared Laser Powered Homogeneous Pyrolysis (IR LPHP). From the IR LPHP of triethylgallium, diethylgallane and monoethylgal- lane have been identified as the major primary products by IR and 1H NMR spectroscopy of both the native species and their adducts with trimethy- lamine. Mixtures of vapours of trimethylamine alane and trimethylgallium, and of trimethylamine alane and triethylgallium have been studied. The spectroscopic analysis confirmed the existence of rapid ligand exchange reactions, and the results of the pyrolysis studies have been related to recent results using these mixtures as precursors to Al2Ga1_2As. Vapour phase infrared spectra of monomeric trimethylaluminium and its perdeuterated isotopomer have been obtained using a slightly modified arrangement of the IR LPHP process. In this, infrared spectra were recorded in the presence of the laser radiation. The infrared and Raman spectra of dimethylaluminium hydride and its partially deuterated isotopomers have been recorded and assigned. On the basis of variable temperature studies and coupled with isotope shifts, it was shown that the vapour phase infrared spectrum at room temperature may be interpreted as predominantly that of the dimer, with smaller amounts of trimer. The laser pyrolysis of dimethylaluminium hydride and its deuterated isotopomers have also been investigated. Methane and dimethylaluminium fluoride were identified as the dominant products, and the formation of trimethylaluminium as an intermediate was observed. Analysis of the isotopic form of the methane suggested that the presence of aluminium hydride bonds assisted in the clean elimination of methyl groups.

During bandgap exposure, the initial steps of latent image formation in the silver halides are dominated by the shallow trapping of free carriers (electrons and holes). Electron Spin Resonance studies of irradiated silver halides in powder, single crystal and de-gelled emulsion formats revealed signals assigned to electrons shallowly trapped at intrinsic sites. These signals were only observed at temperatures below ca. 50K. Experiments were carried out to probe the nature of these sites which appeared to be concentrated at structural dislocations in the lattice. The shallowly trapped electron signal was detected in silver bromide, silver chloride and a range of binary halide silver halide powders. The observation of this signal was accompanied in many cases by the simultaneous observation of a Cyclotron Resonance transition of free conduction band electrons. In addition doping with divalent lead ions capable of acting as "extrinsic" shallow traps resulted in an enhancement of the lifetime of the trapped electron ESR signal. The radiolytic formation of silver atoms and charged clusters (dimers, trimers and tetramers) in frozen solutions of silver perchlorate in methanol, were studied by ESR, this work includes the probable identification of the novel pentameric unit, Ag54+. The formation and detection of clusters of this type in the silver halide matrix is also discussed, together with the detection of latent image centres at liquid helium temperatures, where ionic motion does not occur.

Basic photochemistry, the photoreactions of carbonyl compounds and the mechanisms involved in photo-oxygenation reactions are surveyed. The photochemical reactions of alpha-keto-acids and esters are reviewed. Fran photophysical and decarboxylation studies of alpha-keto-acids and esters in degassed solution, the direct photo induced decarboxylation reaction is shown to occur via a bimolecular electron transfer reaction as opposed to a Norrish Type I fragmentation. The addition of triplet quenchers enhances the decarboxylation reaction via a mechanism suggested to involve radical processes. The proposed mechanisms are substantiated by using electron acceptors to sensitize decarboxylation. The finding that t-butyl pyruvate is photostable in degassed solution and has a much longer lifetime than other alkyl pyruvates, together with triplet quenching studies, shows that alkyl pyruvates fragment from the triplet state via Norrish Type II process. Fran photophysical, quenching and product studies in degassed solution, the Norrish Type II reaction of long chain alpha-keto-acids and esters occurs from the excited singlet state. alpha-Keto-acids and esters undergo direct photo-oxidative decarboxylation, leading to higher yields of carbon dioxide than under degassed conditions. Decarboxylation of pyruvic acid occurs from both the C-1 and C-2 positions. Singlet oxygen does not appear to be involved and a mechanism mediated via electron transfer, with per-acid intermediates, is postulated. In accord with the proposed mechanism, the decarboxylation can be sensitized by electron acceptors. The dye-sensitized photo-oxygenation of alpha-keto-acids and esters proceeds via a mechanism involving dye-acid/ester interaction rather than a singlet oxygen mediated process. Kinetic studies and solvent isotope effects lend credence to the proposed mechanism. The reported results confirm that photochemical alpha-cleavage of the bond linking the carbonyl groups in 1, 2-dicarbonyl compounds is an unfavourable process.

No description available.

Three novel macromonomer systems have been synthesised, characterised and free-radically polymerised. Both copolymerisations and homopolymerisations have been studied. The macromonomers are vinylbenzyl-terminated poly(methyl methacrylate) (PMMA), vinylbenzylterminated poly(butyl methacrylate) (PBMA) and vinylbenzoyl-terminated poly(ethylene oxide) (PEO). The PMMA (number average molar mass 1.4 x l03g!mol) and PBMA (number average molar mass 1.8 x 103 g!mol) macromonomers were synthesised by the same method. This involved the solution free-radical polymerisation of MMA or BMA in the presence of matched initiator and chain transfer agent (4,4' -azobis( 4-cyanovaleric acid) (ACV A) and thiogycollic acid (TGA), respectively). This produced monofunctional carboxyl-terminated prepolymers which were subsequently converted to acyl chloride-terminated prepolymers using oxalyl chloride. This was then combined with pre-synthesised vinylbenzylamine in the presence of triethylamine, to produce vinylbenzyl~terminated macromonomer. The PEO macromonomer (number average molar mass 2.1 x 103 g!mol) was produced by combining commercially available hydroxyl-terminated PEO with pre-synthesised 4-vinylbenzoyl chloride in the presence of triethylamine. All three macromonomers were each free-radically homopolymerised using 2,2' -azobis(isobutyronitrile) (AIBN) as the initiator. The PMMA and PEO macromonomers were studied in more detail in order to establish their solution polymerisation behaviours. This was achieved by carrying out several polymerisations using different initial macromonomer and initiator concentrations. Solution copolymerisations of all three macromonomers with maleic anhydride were also attempted in order to produce altemating single graft copolymers. Maleic anhydride was chosen as the comonomer on the understanding that stYrene produces altemating copolymers with it. The vinylbenzyl-terminated PBMA and PMMA macromonomers were shown to produce graft copolymers containing approximately a 0.5 : 0.5 molar ratio of macromonomer : maleic anhydride, regardless of the initial feed concentrations of the two. All polymers were characterised by gel permeation chromatography (GPC) and IH nuclear magnetic resonance spectroscopy eH NMR). Fourier transform infra-red spectroscopy (FT-IR) was used to characterise the carboxyl-terminated and acyl chloride-tenninated PMMA and PBMA prepolymers, as well as all three macromonomers. A selection ofPMMA graft copolymers were further characterised by solution viscometry and 13CNMR.

No description available.

New insights into the kinetic and molecular dynamics of liquids are presented through two distinct experimental studies. The kinetics and dynamics of cold 12 molecules scattered off liquid polydimethylsiloxane are studied. Time resolved LIF spectra give number densities and quantum state populations throughout both the inelastic scattering and the trapping/ desorption processes. The vibrational cooling of inelastically scattered molecules indicates different mechanisms for the trapping and desorption processes. Surface temperature dependence yields desorption enthalpy 23 - 30 kJ moZ-1 and frequency factor 108 - 1010 Hz, thus suggesting predesorption diffusion. Dynamical behaviour indicates more than one mechanism for activation of trapped species, i.e., conversion of internal energy into translation and energising via interaction with liquid molecules. The molecular dynamics of vertical liquid jets produced by slit nozzles was determined. The alignment of rhodamine 6G molecules, seeded in ethylene glycol jets, is evaluated through polarised laser induced fluorescence (PLF). Computational fitting and integration produce the corresponding liquid velocity distributions. Different streams within the jets are identified. The study is extended to the alignment inside the nozzle. An asymmetric nozzle flow is studied in order to verify the conclusions drawn. An interpretation of the lobed jet kinetics and molecular dynamics is proposed by relating the velocity distributions with the jet horizontal sections.

Two types of mesoporous molecular sieves, MCM-41 and MMS, were prepared, fully characterised and tested as solid acid catalysts and catalyst support materials. Three different methods for characterising the surface acidity of these solid acids were examined and compared. These methods were 1. Fourier Transform infrared (FTIR) spectroscopy of adsorbed pyridine, 2. Pulsed ammonia adsorption using a combination of thermogravimetry and differential scanning calorimetry (TG/DSC), and 3. Temperature-programmed desorption of amines. The acidity results of these molecular sieves were compared with zeolites and acid-treated clays. The Lewis and Br0nsted acid catalytic activities of the ion-exchanged aluminosilicate mesoporous molecular sieves were investigated in liquid phase Friedel-Crafts alkylations. Three model reactions were used to examine the Lewis and Br0nsted acid catalytic activities of the catalysts and the results were compared with acid-treated clays. Generally, the two aluminosilicate molecular sieves showed similar Br0nsted and Lewis acid catalytic activities. The Fe3+ exchanged catalysts showed high Lewis acid catalytic activities while H+ and AI3+ exchanged catalysts showed high Br0nsted acid catalytic activities. In addition to liquid phase Friedel-Crafts reactions, a new technique was developed to monitor the acid catalytic activity of catalysts. The use of temperature programmed-solid insertion probe-mass spectrometry (TP-SIPMS) for this application was investigated. The results were compared with zeolites. The catalytic results from this technique were found to have good correlation with the liquid phase Br0nsted acid catalytic test. Finally, the mesoporous molecular sieves were used as support materials for Lewis acid catalysts. Again, the catalytic activities of these catalysts were studied using a Friedel-Crafts alkylation reaction. The results were compared with some commercially available supported catalysts. Among these catalysts, FeCl) supported on MCM-41 was found to be very active while ZnCb supported on MCM-41 exhibited milder Lewis acid catalyitc activity. However, ZnCb was found to be more dependent on the nature of support.