The generation & high resolution spectroscopic detection of free-radicals in the gas phase
The assignment and analysis of high resolution spectra of transient species in the gas phase leads to the unambiguous identification of the carrier of the spectra. Such spectra can only be observed provided a detectable steady state concentration, depending on the particular spectroscopic technique being employed, can be generated. The first half of this thesis is concerned with three methods of producing detectable concentrations by utilising (i) microwave discharge, (ii) electrical discharge, (iii) carbon dioxide laser photolysis with an associated photosensitiser, sulphur hexafluoride. The high resolution electron paramagnetic resonance spectra of iodine and fluorine atoms and the sulphur monoxide and nitrogen difluoride radicals serve as examples of species produced by these methods and some characteristics of the laser photolysis technique are described in Chapter IV. The advent of the infrared semiconductor diode laser and also a solid state millimeter wave source (an IMPATT oscillator, in conjunction with the technique of magnetic resonance) has led to the development of more sensitive high resolution spectroscopic techniques. High resolution spectra of the important silicon monohydride radical have been observed using the former technique and the experiments and subsequent analysis are described in Chapter VI. The millimeter wave magnetic resonance spectrometer designed and constructed by the author is described in Chapter VII, together with the millimeter wave magnetic resonance spectrum of the oxygen molecule, the first spectrum to be observed by this new technique.