Resonance Ionization Mass Spectrometry of Calcium

Land, Adrian Philip (1990) Resonance Ionization Mass Spectrometry of Calcium. PhD thesis, University of Glasgow.

Abstract

This thesis describes the design and development of a new Resonance Ionization Mass Spectrometer instrument at the Dept, of Physics and Astronomy, the University of Glasgow, and some of the early laser spectroscopy and mass spectrometry investigations carried out with the instrument. The elemental trace analysis capability of the instrument has been measured to be better than 1ppm for both rubidium and calcium in complex matrices. Isotopic abundance ratios for calcium have been measured with an accuracy of +/-3% and with a precision of +/-5%. The laser ablation process has been investigated for a calcium metal sample for several ablation wavelengths. A good fit to data was obtained with a simple thermal process model. The laser ablation of calcium was observed to display a strong enhancement at a wavelength corresponding to a known two-photon resonant, one-photon ionization ("2+1") RIS scheme. The potential utility of this Resonant Laser Ablation process as an analytic technique is discussed. The laser ionization spectroscopy of calcium has been investigated over the wavelength region 413nm to 437nm. Two series of "2+1" transitions were observed, both displaying a strong ion yield enhancement in the vicinity of an intermediate resonace. Single photon, bound-bound transitions from excited states were also observed. The populating mechanisms and relative populations for these excited states have been investigated. A further series of observed lines has been assigned to two-photon resonant transitions from excited metastable states to autoionization levels, lying above the first ionization potential. Several spectral features have not yet been identified, possible mechanisms are discussed. A simple theoretical model for determining two-photon transition cross-sections is outlined. A population rate equation model has been developed to describe the dynamics of the resonance ionization process. These two theoretical models have been combined to generate theoretical ion yields for a "2+1" RIS scheme, a comparison with experimental data is presented. Mass spectra for a calcium metal sample have been obtained using several 'competing' analytic techniques: Laser Ionization Mass Analysis (LIMA) - Resonant Laser Ablation (RLA) - Non-resonant post-ionization of laser ablated neutrals (SALI) - Resonant post-ionization of laser ablated neutrals (RIMS) Significant differences in the observed selectivities, and consequent sensitivities, are discussed with regard to the analytic utility of each technique. The work on the laser spectroscopy and the mass spectrometry of calcium is solely that of the author.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Applied physics, Optics
• Date of Award: 1990
• Depositing User: Enlighten Team
• Unique ID: glathesis:1990-78147
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 15:39
• Last Modified: 30 Jan 2020 15:39
• URI: https://theses.gla.ac.uk/id/eprint/78147