Gossan, Felicity Edith; (2019) Investigations of the reactivity of energised species and the development of a new radical source for surface science. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

‘Energised species’ is a broad term that encompasses a number of different chemical entities. Three specific types of energised species are investigated in this thesis: anions, dications and radicals. These three chemical groups are relevant in a variety of media, ranging from the planetary ionospheres to industrial plasmas. The study of dications, anions and radicals is therefore crucial to further our understanding of the physical and chemical processes occurring in these environments. This thesis divides into two distinct thematic branches. The first branch describes the development of a pure source of free radicals for radical-surface chemistry. A novel piece of equipment, RISA, has been built at UCL that can produce a pure beam of radicals. The pure radical source is coupled to an ultra-high vacuum surface science chamber, which enables the study of radical-surface chemistry. These studies will be used to further our understanding of the interstellar medium and in key industrial processes. The building, optimisation and commissioning of this apparatus is described in this thesis, alongside some proof-of-principle results. The generation of an O radical beam is described in detail. The commissioning of each component of the apparatus is also described. A key step in producing a radical beam with the RISA apparatus is the production and manipulation of an anion beam. The generation of O- and SF5- beams are described. The second thematic branch of this thesis reports the interactions between doubly-charged positive ions and neutral gases. Dications are thought to be important reactive species in ionospheres and interstellar environments, and understanding their reactions is key to furthering our understanding of such media. The investigations of the bimolecular reactivity of Ar2+ and SO2+ with a variety of neutrals are described. A mass spectrometer equipped with a position-sensitive coincidence ion detector has been used to explore the dynamics of these reactions. Reaction energetics and scattering diagrams have been extracted from this data, which has allowed the determination of some interesting, and unusual reaction mechanisms.

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