Aerosol particles are prevalent in the atmosphere and impact the Earth's energy balance through scattering and absorption of incoming and outgoing radiation. Such particles represent one of the largest uncertainties when trying to characterise the anthropogenic causes in the Earth's changing radiation balance. This thesis describes the development of laboratory based techniques for measuring aerosol optical and microphysical properties that are atmospherically relevant. A single particle trapping technique that uses a Bessel-beam propagating counter to a' gas flow (Bessel-beam/gas-flow) is presented. The changing radius of the trapping particle is determined from the collected elastically scattered light. The fluctuating position of a particle trapped along the Bessel beam length is shown to be directly related to the particle radiation pressure efficiency and thus to its radius and refractive index counter to what is expected from , liquid phase optical chromatography measurements. It is shown that ensemble aerosol particle fractionation using a Bessel-beam/gas-flow instrument is not possible. An aerosol ensemble cavity ring down spectrometer (AE-CRDS) was used to determine the refractive index of hygroscopic sodium nitrate aerosols at different relative humidities, A comparison is made between the refractive index retrieved using AE-CRDS and the refractive index retrieved using a single particle, optical tweezers instrument. The accuracy of the optical tweezers refractive index measurement is found to be significantly higher due to the poorly defined size distribution of the aerosol ensemble in the cavity ring down technique. The development of the single particle cavity ring down spectroscopy (SP-CRDS) technique for highly accurate measurements of aerosol extinction efficiencies is presented. The SP-CRDS instrument uses a Bessel-beam/gas-flow optical trap to control the position of a particle within a cavity ring down spectrometer. A new method of accurately obtaining the real part of the refractive index using this technique is described. Measured extinction efficiencies are compared to Mie simulated extinction efficiencies to obtain the refractive index of single component aerosol particles to an accuracy of better than ± 0.1%.

The work presented in this Thesis explores the properties and potential applications of superhydrophobic supports created using electroless deposition of rough silver onto copper wires which were then cut to expose hydrophilic tips. Small aqueous sample droplets were dispensed onto these supports and their Raman spectra were probed either directly or after drying to increase the concentration. It was found that the best way to dispense the droplets, (typically < 1 ul), was to use a pipette whose needle was itself superhydrophobic. When droplets of aqueous glucose, sucrose or mixtures of these were dried they formed viscous dome-shaped deposits in which the sugars were sufficiently concentrated to allow normal Raman measurements to be carried out. With melamine solutions and tear fluid the deposits were dry solids. Detection limits for sucrose, glucose and melamine were found to be 5 x 10-4 M, 2.5 X 10.3 M and 1 X 10.6 M, respectively. The concentration through evaporation approach was combined with surface enhanced Raman spectroscopy (SERS) by drying down droplets containing analyte plus Ag colloid onto the tips of the SHP supports or by making the tips themselves SERS-active by dipping them into AgN03(aq). These methods were tested with exhaled breath condensate (EBC) and adenosine triphosphate (ATP) solutions. The SHP supports could also be used simply as small sample holders, this was tested using colloid droplets to allow SERS of analytes to be recorded without evaporation. The small volumes of material used meant that the absolute detection limits of t he analytes which were investigated were ext remely low. For DNA the det ection limit was 75.9 ng, which is the amount of DNA found in 12 cells. For DPA the detection limit was the amount of material found in 18 spores but PLS calibration of the data allowed quantitation at < 10 spore levels.

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Dielectric spectroscopy is extensively used to measure the level of viable biomass during fermentations but can suffer from interference by a variety of factors including the presence of dead cells, bubbles, electric and magnetic fields, changes in the medium composition, conductivity changes and the presence of non-cellular particles. Three different approaches were used to overcome these problems. The first involved the separate measurement of the spectra of the interferent and the cells. If the spectra were significantly different then spectra containing the signals of both cells and the interferent could be deconvoluted to separately determine the relative contribution of the cells and the interferent to the spectra. This deconvolution approach was successfully used to estimate the biomass levels of yeast in the presence of spent grains of barley and hardwood in the medium. A similar approach allowed the interference of electrode polarisation on spectra of yeast and microalgae to be compensated for. An attempt to determine the concentration of non-viable cells in a mixture of dead and live cells was less successful because the signal of the non-viable cells was quite small compared to that of viable cells. A second approach involved the use of a filter to keep the interferent away from the probe surface. This was used successfully in the measurement of the yeast concentration in the presence of spent barley grains. A third approach involved the use of a second sensor in addition to the biomass sensor. This allows the signal of the biomass sensor to be compensated for the interferent. In one set of experiments microelectrodes were developed which were able to confine the electric field to a small volume near the electrode surface. Covering the electrode surface with a gel or a membrane stopped cells from entering this volume whilst allowing medium to diffuse through. This allowed the measurement of changes in the electrical properties of the medium without a contribution by the cells. Whilst this approach worked, the response time was too long for practical use. More successful was the simultaneous measurement of the biomass with an infrared optical probe and a dielectric probe. It was found that the signal of the optical probe was independent of the cell viability, whilst the dielectric probe was quite insensitive to non-viable cells. The combined use of the dielectric probe and the optical probe allowed the culture viability to be determined in a straightforward manner.

In this thesis a systematic study of the structures adopted by the trimethyl compounds of the Group III elements under a variety of conditions is described. Oligomerization is a feature of common and apparently irrational occurrence amongst these compounds and the investigation was undertaken with the aim not only of determining the structures themselves but also of elucidating the factors influencing structure within the series. The investigation is presented in four main sections: Introduction (Chapters 1 and 2), Experimental (Chapters 3, 4 and 5), Results (Chapters 6, 7 and 8) and Discussion (Chapter 9). The background to the problem is discussed in Chapter 1. Previous investigations of the Group III trimethyl compounds have been haphazard and have concentrated, in general, on the elucidation of the structure of one compound in one phase. The fluid phases have received most attention and whilst trimethylboron, trimethylgallium and trimethylindium are all monomeric, the aluminium compound adopts a symmetrical dimeric structure with bridging methyl groups. In the former three compounds the MC₃ skeleton is planar and, since the methyl groups are able to rotate freely, the overall point group of the molecules is D_3h; the trimethylaluminium dimer belongs to the D_2h point group. The structure of trimethylthallium in the fluid phases has not been reported. In the solid state trimethylaluminium has been shown by X-ray crystallography to retain the bridged, dimeric structure, whereas trimethylindium adopts an unusual structure with a polymeric network of tetramer units in which each indium atom is penta-coordinated by methyl groups. The tetrameric unit is held together by unsymmetrical methyl bridges and the tetramers also interact, but wore weakly. Within each tetramer nearly trigonal Me₃In 'monomer' units can still be distinguished and the binding within these units is much stronger than the binding between them. Thus the strength of the methyl group to indium bonds in the trimethylindium crystal falls in the order: Intra-'monomer', intra-tetramer > inter-tetramer. Recently trimethylthallium has been reported to adopt a similar solid state structure, but with more nearly equivalent inter and intra tetrameric bonds. For both trimethylindium and trimethylthallium the point group of the tetrameric unit is S₄ and the overall symmetry of the crystal is C⁴_4h. The structures of trimethylboron and trimethylgallium in the solid state have not been investigated. The concept of electron deficiency in the context of the present investigation is briefly discussed and the factors conceivably influencing the equilibrium: n (monomer) ? oligomer are considered in some detail. For the specific case of dimer formation five factors arc isolated and, as far as possible, their relative importance assessed for each of the Group III elements:</p> <ol type="I"> <li>the M-M distance in the dimer;</li> <li>the M-C bond enthalpy;</li> <li>the s→p promotion energy;</li> <li>the van der Waals repulsion between non-bonded atoms in the dimer;</li> <li>the stability of the monomer.</li> </ol> <p>In the light of these factors it is concluded that the relative tendency amongst the trimethyl compounds of the Group III elements towards dimer formation in particular, and oligomer formation in general, is given: Al > In > Ga ? Tl ? U The requirements of the technique for structural elucidation are considered:</p> <ol type="i"> <li>applicability to all three phases;</li> <li>applicability over a very wide temperature range;</li> <li>feasibility of examining highly reactive compounds;</li> <li>adaptability to special circumstances (e.g. matrix isolation);</li> </ol> <p>and it is concluded that only vibrational spectroscopy is able to meet all these stringent requirements. In consequence the techniques of Raman and infrared spectroscopy were used almost exclusively in the structural investigations described in the thesis. The interpretation of the spectroscopic results is briefly discussed and the value of vibrational spectroscopy as a structural tool critically reviewed in Chapter 2. The solid state is given particular attention and it is concluded that the level of sophistication appropriate to the interpretation of the spectra of solid compounds is dependent upon both the nature and degree of intermolecular interaction involved. The structure of solid trimethylindium is used to exemplify three distinct approaches to the interpretation of solid-phase spectra:</p> <ol type="i"> <li>the site symmetry approach;</li> <li>the aggregate unit approach;</li> <li>the factor group approach.</li> </ol> <p>By way of introduction to the experimental section of the thesis, the general problems involved in the examination of compounds which react avidly with oxygen and moisture are discussed. The salient features of the instruments used in the investigation are then described. A Cary 81 spectrophotometer equipped with either a helium-neon or an argon-ion laser was employed to obtain the bulk of the Raman data. A Perkin-Elmer 225 spectrophotometer and a Beckman I.R.11 spectrophotometer were used to obtain the infrared spectra in the 4000-200 cm^-1 and 600-50 cm^-1 regions, respectively. The chapter is concluded by a description of the experimental assemblies developed during the course of the investigation for the examination of the Raman spectra of liquid samples over the temperature range -150 to +150°C and for the examination of the infrared and Raman spectra of solid samples at -196°C. The preparation and manipulation of the five compounds are described in Chapter 4, together with details of the simpler sampling devices developed during the course of the investigation. In Chapter 5 the nature, scope and validity of the matrix-isolation method in the context of the present investigation are discussed in SORO detail. It is concluded not only that the method provides a powerful and valid tool for the investigation of the structures of both stable and unstable species but also that, by allowing the matrix to become mobile, it is possible to use the method to follow oligomerization processes in a novel and potentially highly-informative way. The experimental assembly and technique for the examination of the infrared spectra of species isolated in noble gas or nitrogen matrices at 20°K are described. The assembly comprises in essence a Perkin-Elmer 225 spectrometer coupled to a miniature Joule-Thomson liquid hydrogen cryostat bearing a caesium iodide window and encased within a suitable vacuum system. The potential advantages of obtaining the Raman spectra of matrix-isolated species are discussed and the development of an assembly for use in conjunction with the Cary 81 instrument is described. The results of the fluid-phase investigations are presented in Chapter 6. The infrared and Raman spectra of pure trimethylboron wore fully examined at room temperature and, in the case of the Raman spectrum, at temperatures down to -150°C, no change in the spectrum being detected. Trimethylaluminium was examined both pure and in solution at room temperature and, in the case of the Raman investigation, at elevated temperatures both in solution and in the vapour phase. In particular, it proved possible, by examining the vapour at 170°C, to obtain the major features of the Raman spectrum of monomeric trimethylaluminium for the first time.

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Bacterial attachment and aggregation play a vital role in both the formation of biofilm and the removal of undesired biofilms from mineral surfaces. The binding forces involved in this process consist of weak interactions, such as Vander Waals's forces and electrostatic interactions. Although attachment of bacterial cells to mineral surfaces is mainly governed by exopolymer alginate, lipopolysaccharide chemistry seems to play a role in adherence and biofilm accumulation. The project aims to use the synthetic poly (acrylic acid) (PAA) as a model for more complicated biopolymers. Because macromolecules are non-fluorescent, they have been covalently attached with fluorophores, such as ACE, AMMA and AmNS. In an effort to understand the Cell-Mineral Interface process more fully, spectroscopic techniques have been used to investigate conformation and dynamics for PAA, alginate, and lipopolysaccharide (LPS) in both, bulk solution and onto alumina and silica surfaces, which should act as model systems for bacterial growth. Initial solution dynamics of these macromolecules show that the model polymer and biopolymers exhibit partially coiled conformations at low pH values, but adopt a relatively expanded shape from around pH more than their pKa. The addition of simple electrolytes like NaCl and CaCl2 to either system encourages the coiling of the polymer chain at high pH values. Furthermore, adding calcium chloride causes a much tighter coil, and PAA is the most ionic strength responsive polyelectrolyte. A combination of fluorescence and ICP-MS demonstrated that PAA had a strong adsorption affinity for A12O3, in contrast to the alginate and LPS adsorb weakly to the surface. And all polymers attract feebly to the SiO2. The adsorption process is pH dependent: strong adsorption was observed at low pH. The dependence of adsorption on the minerals (A12O3 and SiO2) concentration was also examined at different pH conditions: the adsorption amount was observed to increase by increasing the solid concentration. Adsorption isotherms obtained at low and high mineral concentrations were found to be Henry in type.