Davies, Julia Ann; (1995) Electron spectroscopy of selected atmospheric molecules and hydrocarbons. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The thesis presents experimental results obtained by electron impact energy-loss spectroscopy. Differential oscillator strengths (DOS) of selected atmospheric molecules and hydrocarbons and vibrational excitation cross sections of ozone are measured. A critical comparison with earlier experiments and theory (where it exists) is made. The thesis is arranged in seven chapters. The first discusses molecular structure, spectroscopy and electron-molecule scattering as is relevant to the scope of this thesis. The next two chapters describe the experimental apparatus used. A high resolution electron spectrometer produces an electron beam (∼10 nA) incident upon the molecular target. Scattered electrons of selected energy-loss and scattering angle are detected by the spectrometer providing a total apparatus resolution of ∼50 meV. The vacuum system, gas inlet system and power supplies are also discussed. Chapters 4, 5 and 6 contain the main results obtained during postgraduate studies. DOS of selected atmospheric molecules (O2, N2, N2O, CO and CO2) are presented and critically compared with previous optical and synchrotron studies. Good agreement between results validates the experimental apparatus and techniques used in this work. A detailed study of the DOS of small alkanes (CH4, C2H6, C3H8 and C4H10) and small alkenes (C2H4, C3H6 and C4H8) shows similarities and trends in these series. DOS of ozone, O3, are also measured and the vibrational excitation of ozone is investigated as a function of scattering angle (40° ≤ &thetas; ≤ 120°) and inccident energy (3 eV<T<7 eV) providing some evidence for resonance formation. The thesis concludes with a discussion of preliminary DOS data for chlorine dioxide (OClO), a stratospheric molecule of importance in ozone chemistry. Suggestions for future work, such as an investigation into the effects of temperature on DOS spectra for atmospheric molecules, are also presented.

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