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A pulsed beam of polarised electrons has been successfully produced by means of spin exchange collisions between the atoms of a polarised atomic beam and groups of initially unpolarised electrons trapped in the atomic beam. In several experimental runs electron polarisations of more than 0.5 were indicated at electron trapping times as low as 5 Although the residual ?7 gas pressure in the electron trap was probably more than 10 torr, there was no conclusive evidence of the presence of spin relaxation effects. Reassessment of the design of the present apparatus in the light of the experimental results suggests that the intensity of the trapped electron beam will he significantly increased after suitable modifications are made to "che electrode system which removes the electrons from the electron trap. Once this problem and the problem of atomic beam stability have been solved, this technique should yield highly polarised pulsed beams of electrons at useful intensities. The limitations of the present apparatus as a means of measuring accurately the spin exchange cross sections for collisions of eleotrons with alkali atoms would be significantly reduced in an apparatus specifically designed to give as much direct information as possible about what is happening within the electron trap from the point of view of the electrons, the atomic beam and the residual gases.

This work is concerned with the investigation by electron spin resonance (e.s.r.) of organic free radicals in solution. All the radicals investigated contained oxygen functional groups and were all produced by one-electron oxidation or reduction. The thesis is presented in five Parts, Part 1 being an introductory Part in which the basic principles of e.s.r. are discussed and the apparatus described. A flow apparatus, which is able to detect transient free radicals with lifetimes of ca. 10^-2 sec., is described; this apparatus has been used to detect many of the radicals investigated in this work. Part 2 describes the oxidation of monohydric phenols, ArOH, by a one-electron oxidising agent, ceric sulphate, to produce phenoxy radicals, ArO^•. The e.s.r. spectrum of the unsubstituted phenoxy radical itself, PhO^• , has been recorded, together with the spectra of some 50 other substituted phenoxy radicals. In a large majority of cases the spectra have been analysed successfully and coupling constants, arising from interaction of the free electron with both the ring protons and the α-protons of alkyl-substituents, have been obtained. It was found that the total spin density associated with the ring carbon atoms C₂-C₆ is ca 0.80, thus indicating that ca. 20% of the spin density is associated with the phenoxy oxygen atom and the carbon atom to which it is attached. Qualitative trends in the coupling constants of the ring protons were observed and discussed; for example, it was found that the algebraic sum of the ortho and meta coupling constants was approximately constant with different substituents at the para position. This would suggest that the only effect of the para substituents is to cause a redistribution of the spin density between the ortho and meta positions. Part 3 describes the oxidation, both with potassium ferricyanide in alkaline solution and with ceric sulphate in acid solution, of resorcinol and substituted resoroinols, using the flow apparatus in each case. Different spectra were obtained from the oxidation of the same resorcinol under the different conditions.

In contrast to the large number of measurements which have been made of the transition probabilities of electric dipole allowed spectral lines, there have been very few experimental determinations of the absolute transition probabilities of electric dipole "forbidden" lines. The radiative lifetimes of the metastable states from which forbidden radiation is emitted may be as long as one second or more and in most laboratory spectral lamps such species are destroyed by collision processes before forbidden radiation can be emitted. However, metastable atoms and molecules play important roles in determining the energy balance of the upper atmosphere and many of the prominent spectral features of the aurorae and the airglow are forbidden by the selection rules for electric dipole radiation. An experimental determination of the radiative lifetime of the ¹S₀ metastable state of atomic oxygen is presented in this thesis. The principal emission from this state is the electric quadrupole 2¹S₀ - 2¹D₂ line at 5577&Aring;, which is one of the strongest features of the auroral spectrum. The metastable states of oxygen were populated in a pulsed low current discharge through moderate pressures of either neon or argon which were mixed with a trace concentration (typically 10^-4 torr) of oxygen. In such a discharge, oxygen molecules are dissociated by collision with metastable inert gas atoms and the oxygen atoms so produced are excited to the metastable levels by electron exchange collisions. Atomic recombination is slow so that the oxygen is present mainly in the atomic form. The intensity of the 5577&Aring; forbidden line was recorded as a function of time during the afterglow period which followed a discharge pulse. The light was detected by a photomultiplier tube and the individual photoelectric events were recorded by the multi-channel scaling technique. The channel address cycle was initiated at the end of each discharge pulse and the photopulses were then counted as the channels of the multiscaler were successively addressed during the afterglow period. In this way, the intensity detected from the afterglow was obtained as a function of channel number or time. The statistical scatter on the recorded signal was reduced by adding the intensities detected from many afterglow cycles. During the late afterglow, the decay of the metastable state population was exponential with decay constant &Gamma; = ^A&prime;&frasl;_p + &Gamma;₀ + &alpha;&prime;p + &beta;&prime;p + &alpha;&prime;_op_o where the terms represent respectively diffusion to the walls of the vessel, the reciprocal &Gamma;₀ of the 0(¹S₀) radiative lifetime and deactivation of metastable atoms during two and three body collisions with both inert gas atoms and oxygen atoms. Here p and p_o are the partial pressures of the inert gas and of atomic oxygen respectively, and the coefficients &alpha;&prime;, &beta;&prime; and &alpha;&prime;_o are the rate constants for the different collisional deactivation processes. A large volume discharge vessel and inert gas pressures of typically 10 torr were used in order to reduce the loss of metastable population by diffusion. The spectroscopically pure gases used in the experiments were mixed in a bakeable gas handling system. The oxygen partial pressure could not be measured directly because of adsorption of atomic oxygen on the walls of the vessel. Instead, the effect of the 0(¹S₀) deactivation by atomic oxygen was estimated by correlating the measured decay constants with the observed intensity of the afterglow signal. This intensity decreased as the oxygen was adsorbed. A "reduced" decay constant was determined at each inert gas pressure investigated as the value which would be expected at zero signal intensity or zero oxygen pressure. Afterglow curves were recorded using both neon and argon at pressures ranging between 1 torr and 40 torr and the radiative lifetime of the 0(¹S₀) metastable state was evaluated by correlating the values of the reduced decay constants obtained at different inert gas pressures. The result &deg;C_expt [0(¹S₀)] = 0.76 &plusmn; 0.03 seconds is considerably more accurate than the previous experimental determinations and is in good agreement with the best theoretical estimate &deg;C_theory [0(¹S₀)] = 0.80 seconds Furthermore, the result is the first experimental determination of a metastable state radiative lifetime which is sufficiently reliable to be compared to theoretical estimates. Measurements were also made of the coefficients for diffusion of 0(¹S₀) metastable atoms through neon and argon, and the rate constants for deactivating collisions with neon and argon. The products of the inert gas pressure and the diffusion coefficients were determined as 416 &plusmn; 12 torr cm² s^-1 for neon at 298&deg;K, and</li> <li>268 &plusmn; 8 torr cm² s^-1 for argon at 298&deg;K in good agreement with previous measurements. These results are consistent with a Lennard-Jones collision diameter of 2.85&Aring; and a force constant &epsilon;/k = 21.7&deg;K for elastic collisions between two 0(¹S₀) atoms. Upper limits on the rate constants for two body deactivating collisions between 0(¹S₀) atoms and inert gas atoms were determined as 4 &times; 10^-19 cm³ s^-1 for neon, and 5.5 &times; 10^-18 cm³ s^-1 for argon. Deactivation during three body collisions was found to be insignificant compared to the other loss processes.

The characterisation and commissioning of a new molecular beam apparatus is described. This equipment was designed to have the capability of observing coincidence signals between photon emission detection and scattered particle detection resulting from ion-molecular and ion- atom collisions. Early experiments involving the observation of photon emission, which resulted from non adiabatic charge exchange processes in He<SUP>+</SUP>/Ar collisions, are detailed, A mechanism is proposed for the excitation of the <SUP>2</SUP>p <SUP>o</SUP> and <SUP>2</SUP>D <SUP>o</SUP> states of Ar<SUP>+</SUP>. in those collisions. Excitation resulting from charge exchange processes in the He<SUP>+</SUP>/HC1 collision system are also described. In particular a strong non Franck-Condon effect is observed in the excitation of the HC1<SUP>+</SUP> A <SUP>2Σ+</SUP> state. The unexpectedvibrational population of the HC1<SUP>+</SUP> A <SUP>2Σ+</SUP> state is examinedunder a variety of conditions and is contrasted to the vibrational distribution of that state resulting from collisions between Ar<SUP>+</SUP> and HC1. A mechanism is proposed which accounts for these findings. Finally the principles and execution of the first coincidence experiment are described. This experiment involved the observation of emission from the N<SUB>2</SUB>C<SUP>3πu</SUP>state, excited in collision with He<SUP>+</SUP>, and recording the time differential between the detection of those photons and the detection of the associated scattered ions. The results of this experiment are detailed and suggestions made as to the reasons for our failure to observe a clear result.

Previous assessment of the validity of an approximate force field has been based upon the accuracy with which it reproduced the observed frequencies. This is considered to be unsatisfactory. The present work compares the approximate force field with the harmonic general force field, which is regarded as the most precise description of intramolecular forces. As a preliminary to this, it has been necessary to review both, the methods available for force field calculation, and the different approximate force fields in current use, A consistent set of frequency data and molecular parameters have been compiled, and used to calculate general and approximate force, fields for thirty three molecules of types XY2 bent, XY3 pyramidal and XY4 tetrahedral, Finally, the comparison has revealed that two approximate force fields (Fadini's Stepwise Coupling and Nearest Solution Methods), provide a consistently good estimate of the harmonic general force field, and can therefore be recommended for general use.

The microscopically pumped maser, or micromaser is a cavity QED experiment intended to be a physical realisation of the Jaynes-Cummings model of a single two-level atom interacting with a single mode electromagnetic field. This is the simplest model that describes the interaction between light and matter, yet it predicts behaviour unexpected from semiclassical models, such as the revival of Rabi oscillations of an atom interacting with an initially coherent field and non-monotonic linewidth as a function of pumping. The micromaser at the University of Leeds consists of a high quality superconducting microwave cavity designed to be resonant with the transition between two specific Rydberg states of rubidium. These two states behave like an ideal two level atom, and couple strongly to the cavity field due to a large dipole moment. These Rydberg atoms are passed through the cavity in a rarified beam such that in most instances when there is an atom in the cavity, there will only be one, closely approximating the Jaynes-Cummings model. I present experimental work on the build phase of the micromaser. Specifically I routed all of the wiring and microwave lines in the cryostat that contains the micromaser, and designed mounts for various components. I also designed several testing methods for probing high quality microwave cavity resonances and quality factors which are presented. Using the Jaynes-Cummings model as a prototype, I demonstrate how extensions to the model can be used to construct universal quantum logic gates that operate on photonic qubits in a multi-mode cavity. This could be realised in a micromaser with a multi-mode cavity. Conversely, I demonstrate that by using atoms as qubits, detuned cavities can be used to generate entangled resources such as the Greenberger-Horne-Zeilinger state, the W state, and graph states of atoms. I show that single qubit rotations on Rydberg atom qubits have already been experimentally demonstrated so that in combination these entangled resources are useful for quantum metrology, quantum computation and even tests of quantum gravity.

The aim of this thesis is to investigate the interaction of neutral atoms with conducting and superconducting surfaces. Experimental advances in the magnetic confinement of ultracold atoms have shown that they can act as a powerful tool in a wide range of phenomena such as electric and magnetic field imaging and matter wave interferometry. Coherent manipulation of atoms and ever smaller magnetic traps are essential elements in the implementation of integrated quantum devices for fundamental research, quantum information processing and precision measurements. This thesis considers main influences on atoms placed within three different environments which are useful in achieving miniaturization and efficient control in atomic magnetic traps: carbon nanotubes, dielectric surfaces and superconducting thin films. The possibility of holding atoms near the outside of a carbon nanotubes will be addressed. In order to give a qualitative analysis of the atom-nanotube interaction, thermally induced spin-flips and the Casimir-Polder potential have been considered. The comparison between these two effects is presented in this thesis. It indicates that the Casimir-Polder force is the dominant loss mechanism and an estimation of the minimum trapping distance is given based on its effect. Secondly, a first-principles derivation of spatial atomic-sublevel decoherence near dielectric and metallic surfaces will be presented. The rate obtained for the decay of spatial coherence has dual implications, on one hand, it can be considered as a measure of the coherence length of the fluctuations of the electromagnetic field arising from a given substrate. On the other hand, it turns out to be relevant for quantum information encoding in double well potentials. Finally, the known spin-flip transition rate will be linked to the flux noise spectrum in superconducting thin films showing the feasibility of using cold atomic clouds in the investigation of vortex dynamics.

This thesis reports on the development of novel techniques for the detection and manipulation of cold gases of neutral atoms. The research presented focusses on the implementation of a photonic waveguide chip into an atom optics experiment. Our photonic chip consists of 12 parallel waveguides with a 10 µm pitch and a 16 µm trench in the centre. A wire subchip underneath the photonic chip can create magnetic fields to guide atoms into the trench and hold them there. The electric field of the light mode propagating through the waveguides has a 1/e radius of 2:2 µm. This small light mode can readily be used for local measurements of the atomic density. This thesis describes the setup of the waveguide chip experiment and gives a detailed characterisation of the interaction between light and atoms in the trench. Additionally, I report on a scheme for detecting atoms while minimising the number of scattered photons for a given precision of the measurement. We use a light beam synthesized from two frequencies tuned to either side of the atomic resonance and detect the differential phase shift they acquire when passing through an atomic cloud by referencing the beat between the two frequencies to a local oscillator. Unlike most similar techniques our beam does not contain a carrier signal and can therefore be balanced around the atomic resonance in order to cancel the mean optical dipole force on the atoms.

The Compact Muon Solenoid was designed to make discoveries at the TeV scale : to elucidate the nature of electroweak symmetry breaking and to search for physics beyond the Standard Model. For any such discovery to be credible, it must first be demonstrated that the CMS detector is understood. One mechanism to make this demonstration is to measure "standard candle" processes, such as W and Z production. This thesis describes preparations undertaken to make these measurements using the electron decay modes, with [derivative]Ldt = 10 pb-1 of collision data. The energy resolution of the electromagnetic calorimeter was measured in test beam data. An improved method of deriving the optimised weights necessary for amplitude reconstruction is described. The measurement of electron charge using tracks is impaired by the electron showering in the tracker material. A novel charge measurement technique that is complementary to the existing method was assessed. Missing transverse energy is a powerful discriminating variable for the selection of W+/ -> e+/ [upsilon]e events, however it is difficult to simulate accurately due to its global nature. The Ersatz Missing Energy method was developed to provide reliable and accurate descriptions of missing energy from data using readily reconstructible [gamma]*/Z -> e+e- events. The method is described and evaluated. Finally, the measurement strategy for W and Z boson production cross-sections in early data is outlined and analysed using simulated data. Significant results can be obtained with only [derivative] Ldt = 10 pb-1.