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Title: Equilibrium and kinetic studies of Ca, Mg and Cs atoms in inductively coupled plasmas and by time-resolved measurements in the gas phase using atomic spectroscopic techniques
Author: Clay, Robert Stanley
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1991
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Abstract:
High temperature studies on the metal atoms Ca, Mg and Cs in the gas phase have been carried out using a number of experimental techniques, and include investigations of both equilibrium and kinetic properties. An inductively coupled plasma atomic emission source was set up in Cambridge in order to study emission from electronically excited states of Mg, Mg+, Ca and Ca+, and to demonstrate electronic energy exchange between near-resonant excited states and electron transfer. An important aspect of this work was the investigation of interferences between different metal species in the plasma for analytical purposes. The principal measurements of this nature, however, were carried out on the inductively coupled plasma system at the Shell Thornton Research Centre, Chester. Although no clear trends in emission behaviour could be discerned with the interferents at moderate concentrations, large concentrations of interferents were found to suppress both ionic and atomic analyte emission, and the results were considered in terms of various temperatures and electron density. From the measurements it was possible to obtain a crude estimate of the plasma temperature. Kinetic studies on ground state calcium atoms, Ca(41S0), included the construction of a relatively simple apparatus for time-resolved monitoring of Ca(41S0) atoms by laser-induced fluorescence following their generation by pulsed photolysis of calcium halide vapour at elevated temperatures. These measurements were to be carried out in the presence of a range of gaseous reactants, in a slow-flow system kinetically equivalent to a static system. Initial investigations suggested, however, that the system was limited by laser power and sensitivity, and the technique of time-resolved atomic resonance absorption proved more suitable for these kinetic measurements. Absolute second-order rate data were thus obtained for the reactions of ground state calcium atoms, Ca(41S0), with the collision partners CH3Cl, C2H5Cl, CF3Cl, CF3Br, CF2Cl2, CHFCl2, CH3F, CF3H, CF4, SF6, HCl, HBr, N2O and H2O. This constitutes a new body of absolute rate data, which is of both fundamental interest, and importance with respect to flame chemistry. A significant aspect of the work was the development and construction of a highly intense hollow cathode calcium emission source, operated at high current, and estimated to be more intense than analogous strong emission sources for alkali atoms by a factor of around a thousand. While this novel application of the time-resolved atomic resonance technique to the study of ground state calcium atoms was restricted to measurements at single, elevated temperatures, it never-the-less provides the basis for future kinetic studies on alkaline earth metal atoms. The technique of time-resolved atomic resonance spectroscopy was also used to monitor ground state caesium atoms, Cs(62S1/2) following their generation by pulsed photolysis of a halide precursor at elevated temperature. By this means, absolute second order rate data were obtained for the reactions of Cs(62S1/2) with CF3Cl, CF2Cl2, CFCl3, CCl4, CHFCl2, CH3Cl, C2H5Cl, CF3Br, CH3Br, C2H5Br, CH3F, CF3H, CF4, SF6, HBr and HCl, constituting a new body of rate data, and developing further the area of heavy alkali atom reaction kinetics.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.597752  DOI: Not available
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