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Title: Tunable UV laser-induced photo-fragmentation of selected alkali halides in molecular beams
Author: Bakry, A. H. A.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1994
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This thesis is concerned with two sensitive and selective methods for detecting low concentrations of molecules and reactive atoms. The methods are described in detail, and in particular emphasis is given to the design, construction and operation of systems to implement Resonance Ionization Spectroscopy (RIS) and Laser Induced Fluorescence (LIF) for detecting photodissociated alkali atoms and alkali halide molecules. Alkali halide molecules are often treated as model cases by both theoreticians and experimenters because of their unique properties which distinguish them from other molecules such as the avoided crossing of their lowest two excited potential curves with the ground state potential curve. Molecular beams of sodium iodide, lithium iodide, and caesium iodide, representative for alkali halides, were used as a rich source to study the dissociation and the detection of these molecules. In the RIS experiments, a pulsed tunable UV laser was used to photodissociate NaI, LiI and CsI. Na, Li, and Cs atoms were detected by two-step RIS. This is the first time that RIS on alkali halides has been performed in a molecular beam. The photodissociation of NaI was studied as a function of the UV-wavelength. The result has shown that the dissociation cross section for NaI at the first UV maximum (325nm) is of the same magnitude as the absorption cross section determined by Davidovits et al, 1967. A variety of different experiments were conducted to establish the sensitivity of the technique, and detection limits of 5x106 Na-atoms cm-3, 10^6 Li-atoms cm^-3 and 3x106 Cs-atoms cm-3 were measured. To detect NaI molecules, a molecular beam of NaI was used to demonstrate the technique of LIF. However, no spectrally resolved molecular LIF was observed; explanations for the failure are provided, and in this context factors that affect the detection sensitivity of RIS and LIF are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available