A study of the electronic structure of some atoms and small molecules with high temperature photoelectron spectroscopy
A study of the electronic structure of some atoms and small molecules with high temperature photoelectron spectroscopy
This thesis describes the development of an intracavity frequency doubled dye laser from a commercial Spectra-Physics 380D single frequency ring dye laser, and the application of this system to anumber of spectroscopic studies in discharges. Evaluation of the stability of the laser cavity is carried out, by computer calculation, in order to optimise the optical component set used in the frequency doubled dye laser. Using an ADA (ammonium dihydrogen arsenate) crystal, 17 mW of continuous wave ultra-violet, tunable over the range 292-302 am, has been produced. The linewidth, when the laser is stabilised, is about 500 kHz in the UV. The CW UV output has been used to measure helium triplet (23S) metastable densities in a positive column discharge as a function of pressure (1-8 Torr) and current (2.5-80 mA). A maximum density of ioxlo12cm 3 is measured for a pressure of 2 Tort and current of 60mA. The measured metastable densities are used in a rate equation analysis to extract values of the rate coefficient for destruction (by collisions with electrons) of the 23S metastables (1.6x10®s 1 for p - 2 Torr). A study of the optogalvanic signal generated when irradiating a neon positive column discharge with laser light of wavelength 588.2 xc, corresponding to the 1s5 2p2 transition, is carried out. The signal is found to change sign as the dye laser power is increased, for some discharge conditions. Spatial studies of the optogalvanic signal in conjunction with absorption and emission studies are carried out to investigate the evolution of the population densities of levels connected to the 1s5 and 2p2 levels. A rate equation model is developed which demonstrates the importance of the 183 population density in explaining the observed sign reversal. A high resolution study of two transitions in the UV in the tungsten spectrum, is presented. The even isotope splittings and the hyperfine splitting between the two strongest hyperfine components on transitions at 294.4 in and 294.7 cm have been resolved by saturated absorption spectroscopy. From centre of gravity considerations the hyperfine splittings of the three levels involved in the two transitions have been predicted as 1630 MHz for the 7S3 level, -506 MHz for the 3692 level and 225 MHz for the 3683 level. Simple wavemeter using a corner-cube Michelson interferometer is described. Digital counting circuits to provide a direct reading of either the fundamental or second harmonic wavelength have been designed and constructed. Wavelength readings accurate to 1 part in 610 are achieved. The spectrometer, furnace assembly and induction heating system used for the evaporation of samples and the subsequent recording of their photoelectron spectra at temperatures up to 2600°K are described. The ab initioSCF and Bartree-Fock-Slater (HFS) computational schemes used in analysis of spectra are detailed. The photoelectron spectra of the vapours of tin, germanium and gallium are reported. Bands associated with ionisation from the outermost orbital have been observed from the ground as well as low-lying excited states of these elements, and relative band intensities have been used to estimate the excitation temperatures. For gallium evidence is presented to show that the Hel spectrum is perturbed by an autoionisation process. The Hei and Hell photoelectron spectra of ZnF2 and CUP have been recorded and interpreted with the aid of ab iniEio SCF calculations and a configuration interaction method. Results suggest that the 3d orbitals in CuF2 are valence in character, whereas in ZnF2 they are core-like. The Hell spectra of OF, ThF, UC14 and ThCl4 have been recorded and are campared with Eel and X-ray photoelectron spectra. The results show that the electronic structure of U and Th tetrahalides are similar, both in the solid and vapour phases, apart from the presence of two metal 5f electrons in uranium. The Eel spectrum of the first band of the dimethylsilaethylene molecule is reported and analysed by means of ab initio' SCF and BPS methods. Results are consistent with the presence of a C=Si double bond. Results of some unsuccessful but informative high temperature experiments are given. Details of a new multidetector photoelectron spectrometer are also presented.
University of Southampton
1982
Josland, Graham David
(1982)
A study of the electronic structure of some atoms and small molecules with high temperature photoelectron spectroscopy.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis describes the development of an intracavity frequency doubled dye laser from a commercial Spectra-Physics 380D single frequency ring dye laser, and the application of this system to anumber of spectroscopic studies in discharges. Evaluation of the stability of the laser cavity is carried out, by computer calculation, in order to optimise the optical component set used in the frequency doubled dye laser. Using an ADA (ammonium dihydrogen arsenate) crystal, 17 mW of continuous wave ultra-violet, tunable over the range 292-302 am, has been produced. The linewidth, when the laser is stabilised, is about 500 kHz in the UV. The CW UV output has been used to measure helium triplet (23S) metastable densities in a positive column discharge as a function of pressure (1-8 Torr) and current (2.5-80 mA). A maximum density of ioxlo12cm 3 is measured for a pressure of 2 Tort and current of 60mA. The measured metastable densities are used in a rate equation analysis to extract values of the rate coefficient for destruction (by collisions with electrons) of the 23S metastables (1.6x10®s 1 for p - 2 Torr). A study of the optogalvanic signal generated when irradiating a neon positive column discharge with laser light of wavelength 588.2 xc, corresponding to the 1s5 2p2 transition, is carried out. The signal is found to change sign as the dye laser power is increased, for some discharge conditions. Spatial studies of the optogalvanic signal in conjunction with absorption and emission studies are carried out to investigate the evolution of the population densities of levels connected to the 1s5 and 2p2 levels. A rate equation model is developed which demonstrates the importance of the 183 population density in explaining the observed sign reversal. A high resolution study of two transitions in the UV in the tungsten spectrum, is presented. The even isotope splittings and the hyperfine splitting between the two strongest hyperfine components on transitions at 294.4 in and 294.7 cm have been resolved by saturated absorption spectroscopy. From centre of gravity considerations the hyperfine splittings of the three levels involved in the two transitions have been predicted as 1630 MHz for the 7S3 level, -506 MHz for the 3692 level and 225 MHz for the 3683 level. Simple wavemeter using a corner-cube Michelson interferometer is described. Digital counting circuits to provide a direct reading of either the fundamental or second harmonic wavelength have been designed and constructed. Wavelength readings accurate to 1 part in 610 are achieved. The spectrometer, furnace assembly and induction heating system used for the evaporation of samples and the subsequent recording of their photoelectron spectra at temperatures up to 2600°K are described. The ab initioSCF and Bartree-Fock-Slater (HFS) computational schemes used in analysis of spectra are detailed. The photoelectron spectra of the vapours of tin, germanium and gallium are reported. Bands associated with ionisation from the outermost orbital have been observed from the ground as well as low-lying excited states of these elements, and relative band intensities have been used to estimate the excitation temperatures. For gallium evidence is presented to show that the Hel spectrum is perturbed by an autoionisation process. The Hei and Hell photoelectron spectra of ZnF2 and CUP have been recorded and interpreted with the aid of ab iniEio SCF calculations and a configuration interaction method. Results suggest that the 3d orbitals in CuF2 are valence in character, whereas in ZnF2 they are core-like. The Hell spectra of OF, ThF, UC14 and ThCl4 have been recorded and are campared with Eel and X-ray photoelectron spectra. The results show that the electronic structure of U and Th tetrahalides are similar, both in the solid and vapour phases, apart from the presence of two metal 5f electrons in uranium. The Eel spectrum of the first band of the dimethylsilaethylene molecule is reported and analysed by means of ab initio' SCF and BPS methods. Results are consistent with the presence of a C=Si double bond. Results of some unsuccessful but informative high temperature experiments are given. Details of a new multidetector photoelectron spectrometer are also presented.
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Published date: 1982
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Local EPrints ID: 460598
URI: http://eprints.soton.ac.uk/id/eprint/460598
PURE UUID: 7512ccf9-2591-442e-b7b9-94776aef7f78
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Date deposited: 04 Jul 2022 18:25
Last modified: 04 Jul 2022 18:25
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Author:
Graham David Josland
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