An XPS investigation of the interaction of CH4, C2H2, C2H4 and C2H6 with a barium surface
1982; Elsevier BV; Volume: 123; Issue: 2-3 Linguagem: Inglês
10.1016/0039-6028(82)90334-x
ISSN1879-2758
Autores Tópico(s)Advanced Chemical Physics Studies
ResumoThe generation and pumping of hydrocarbon gases by a barium getter layer in electronic vacuum devices has been investigated by characterizing a barium film in an ultra high vacuum equipment by means of XPS before, during and after exposures to respectively CH4, C2H2, C2H4 and C2H6. The reaction conditions (temperatures and pretreatment of the surface, background pressure and exposure doses) closely resemble those in electronic vacuum devices. The probability that a barium layer will react with CH4 and C2H6 was below the detection limit. C2H2 and C2H4 give rise to the formation of barium carbide compounds and with a high reaction probability. In addition, the interaction with C2H2 reveals the formation of carbon-containing surface complexes. Investigations by means of XPS on the C Is spectral features show the presence of at least two groups of carbon-containing surface complexes, which behave differently in response to moderate heating and to an exposure to water vapour. In cases where oxygen is present at the surface, oxygen-containing (hydro) carbon adsorbates are present too. XPS observations of the behaviour of these surface complexes show similarities with reaction steps in the mechanisms proposed for the hydrogenation of CO in the Fischer-Tropsch synthesis of hydrocarbons. Low-pressure hydrogenation of these adsorbates containing hydrocarbons and oxygen can led to the formation of hydrocarbon gases in electronic vacuum devices.
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