Low energy electron interactions with water

UoM administered thesis: Phd

  • Authors:
  • Rhiannon Monckton

Abstract

Understanding the radiation chemistry of water is important in many disciplines including the nuclear industry, astrochemistry, and medicine. In recent years, low-energy electrons have been paid much greater attention, due to their abundance and reactivity in irradiated materials. Electrons with energies <20 eV may interact via the dissociative electron attachment (DEA) mechanism, which has been found to cause single-strand breaks in DNA.DEA in water involves the capture of a low energy electron by a neutral water molecule into an outer orbital and is generally accompanied by excitation of the H2O molecule, causing it to dissociate. The aim of this work is to study the OH radical produced in DEA to H2O using laser-induced fluorescence (LIF).A high-vacuum chamber equipped with low energy electron gun, molecular beam and laser system was built for gas-phase studies of DEA in water. LIF spectra were recorded from OH formed by dissociation of gas-phase H2O, for determination of the rotational and vibrational state distributions.In addition to the gas-phase studies, low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices were investigated using a combination of temperature-programmed desorption (TPD) and infrared reflection-absorption spectroscopy (IRAS).For CO trapped within approximately 50 mono-layers of the vacuum interface both reduction and oxidation products were observed including HCO, H2CO, H3CO and CH3OH, and CO2. Concentration profiles of CO versus film thickness showed two zones in the film: a near-surface zone of preferential oxidation, and a zone of preferential reduction deeper in the film. A Monte Carlo model was developed based on diffusion of H atoms through the ice lattice, which supported the experimental results.

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Original languageEnglish
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Award date1 Aug 2015