Investigations of the kinetics and dynamics of elementary gas-phase collisional processes and reactions have proved to be of major significance in many areas of both pure and applied physics and chemistry. A thorough understanding, both experimental and theoretical, of the collisional processes of defined quantum states of atoms and molecules is required. This includes physical processes such as energy transfer, collisional quenching, diffusion, charge transfer and ionisation, and chemical processes such as reaction rates, mechanism branching ratios and reaction potential energy surfaces. These topics have long been important in a variety of systems, including atmospheric chemistry, gaseous plasmas, combustion science and developing novel chemical laser systems. The primary motivation for the present work is to extend our knowledge about the collisional behaviour and reaction kinetics of alkaline-earth atoms in specific electronic states. The first part of this thesis (chapters 1-5) is directed towards a kinetic investigation of ground state atoms, in particular, Ca[4s<SUP>2</SUP>(<SUP>1</SUP>S<SUB>0</SUB>)], generated by flash photolysis of gaseous iodide molecules and whose decay is monitored by time-resolved atomic resonance absorption spectroscopy in the 'single-shot mode'. A new body of data for the absolute rate constants for the F, Cl, Br and I-atom abstraction reactions of Ca[4s<SUP>2</SUP>(<SUP>1</SUP>S<SUB>0</SUB>)] with a range of halide molecules are reported. The diffusional behaviour of this atom in noble gases, He, Kr and Xe and also N<SUB>2</SUB>, is also investigated in this work and the diffusion coefficients are consequently presented here. It is envisaged in broader terms that these studies have not only provided some new kinetic data for use in related areas but also contribute to form a framework for theoretical considerations and comparisons between the ground state and excited state reactions involving this atom. It is also considered that this type of research can be helpful in the area of exploring the relationship between reaction rate constants and the atomic or molecular electronic structures. In this work, the influence of molecular structure on the reaction rate when increasing the number of carbon atoms in the alkyl-halide chains is also investigated. Some measurements of the absorption cross-sections of gaseous MI<SUB>2</SUB> (M = Ca, Sr, Ba) molecules by UV radiation as a function of wavelength are also made in this work but are presented in the appendices of this thesis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:599351 |
| Date | January 1998 |
| Creators | Geng, J. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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