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Title: Plasma diagnostics and spectroscopy using tuneable IR diode lasers
Author: Fan, W. Y.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1998
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The first section of this dissertation is directed towards understanding the chemistry of free radicals and other discharge products in low pressure methane and mixed methane plasmas. The behaviour of the discharge products in a 10 kHz parallel plate reactor was investigated through IR diode laser absorption spectroscopy of their rovibrational lines. The behaviour of the methyl radical, CH3 in pure methane plasmas has been reinvestigated and extended and kinetic data relating to some electron impact dissociation reactions have been estimated. Methyl radical concentrations in very dilute methane in hydrogen mixtures (about 1%) have been measured for the first time. Nitrogen dioxide was shown to be a much more efficient scavenger in the plasma than nitric oxide. It was also shown that the CH3 concentration in the plasma did actually increase when oxygen was added in small amounts. The presence of many other species such as C2H2, C2H4, C2H6, CH2O, CH3OH, HCOOH, CO and CO2 in CH4/H2/O2 plasmas have been confirmed and their concentrations measured. A chemical model to simulate these plasmas has been written using a modelling package called FACSIMILE. Good agreement was found between measured and calculated concentrations for most of the species detected. The second section of the dissertation concerns velocity modulation IR spectroscopy of diatomic ions in plasmas. High-J pure rotational lines belonging to HeD+ have been observed using an air cooled ac discharge in helium and deuterium. Thirteen lines in the v=0 and v=1 states between 620 and 720 cm-1 were measured including a bound-to-quasibound transition of HeD+. A least squares fit using both observed and the previously reported lines has given much more accurate constants than earlier work. The IR absorption spectrum of SiCl+ has also been investigated and this ion was generated in a discharge of SiCl4 and He. About 180 lines were observed in the region between 620 and 700 cm-1 and assigned to the fundamental and hots bands of 28Si35Cl+ and its isotopes. A least squares fit of these lines yielded nine mass-independent Dunham coefficients for SiCl+. A potential energy curve for the electronic ground state of SiCl+ has been derived and the dissociation energy for the lowest channel i.e. SiCl+ and Si+ has been determined for the first time.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available