Tuneable far infrared (TuFIR) spectroscopy

• Main Author: Fraser, H. J.
• Published: University of Cambridge 1999
• Subjects: 543.5
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599198

This PhD thesis describes the application of high resolution, Tuneable Far Infrared (TuFIR) Laser Spectroscopy to the study of gas phase radicals and stable species. Following its development in the 1980's there are currently eight groups using TuFIR Spectroscopy world-wide: the Cambridge spectrometer is unique to the UK. Chapter 1 serves as an introduction to the FIR region of the electromagnetic spectrum and highlights the need to develop tuneable, coherent radiation sources for spectroscopy in this region. Non-linear mixing techniques for TuFIR generation are reviewed and compared with the more established microwave multiplication methods. Limitations of TuFIR techniques are mentioned. A review of previous work in TuFIR spectroscopy is given. Chapter 2 describes the experimental and theoretical background to the TuFIR technique, with some mathematical development. The two configurations of the Cambridge TuFIR spectrometer are outlined. Chapter 3 describes the development work that was undertaken by the author to improve the performance of the TuFIR spectrometer. The spectrometer sensitivity, resolution and precision are discussed. These advances are illustrated with TuFIR spectra of SO<SUB>2</SUB>. In Chapter 4 the spectroscopy of BrO is introduced. The role of BrO in ozone depletion is discussed. The importance of line broadening coefficients in deciphering atmospheric data is mentioned. The pressure broadening coefficients of <SUP>81</SUP>BrO in Ar and O<SUB>2</SUB> are determined for the first time. Chapter 5 reports on pressure broadening studies in CHF<SUB>3</SUB>. This molecule is significant for global warming. The self- and air- broadening coefficients of CHF<SUB>3</SUB> are determined and their dependence on temperature and rotational quantum numbers (J, K) investigated. Finally, Chapter 6 outlines the current status of the TuFIR spectrometer. Future development work is considered. Data is presented from preliminary searches for halogenated radicals and the possibilities for studying these, or other short-lived species, are explored.