Reflection-absorption infrared spectroscopy (RAIRS) has been used to probe the interaction of cyclohexane, partially deuterated cyclohexane C<sub>6</sub>HD<sub>11</sub>, toluene and ethylene with the Ni{111} surface. The coadsorption of cyclohexane and oxygen on the Ni{111} surface has also been studied in some detail; the effects of differing coverages of both pre- and post- dosed oxygen on cyclohexane adsorption has been investigated. As these experiments were the first to be completed using a new UHV system, an important element of this PhD project involved commissioning the UHV system, including the LEED and Auger apparatus, and setting up the RAIRS optical system. On the clean Ni{111} surface at 110 K adsorbed cyclohexane exhibits a site symmetry of C<sub>3v</sub> which persists through to the multilayer regime. Adsorbed molecules in the first layer exhibit a broadened and downshifted vCh stretching vibrational band, thought to arise from CH...M interactions and observed on many metal single crystal surfaces. The effect of coadsorbed oxygen on cyclohexane adsorption is strongly coverage dependent. At lower oxygen coverages, θ<sub>O</sub> ≤ 0.25, a further downshifting of the softened vCH stretching vibration is observed, indicating the importance of charge transfer from the filled CHσ orbital to the metal in weakening the C-H bond. Adsorption of cyclohexane on the Ni{111}-(√3x√3)R30°-O surface, θ<sub>O</sub> = 0.33, leads to total suppression of any C-H...M interaction, attributed to blocking of the bare metal sites by the adsorbed atoms. Post-dosing of oxygen on the cyclohexane adlayer leads to compression of existing islands of cyclohexane, involving molecular transfer from the first layer to the second. This is attributed to the difference in heats of adsorption of the two adsorbates.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:296514 |
| Date | January 1995 |
| Creators | Cooper, Elaine |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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