Thin Coronene films on HOPG were oxidized by exposing them to atomic oxygen under ultra-high vacuum conditions. The products were probed by mass-resolved thermal desorption spectroscopy and X-ray photoelectron spectroscopy. The species subliming from thick oxidized films comprise predominantly epoxides C24H12O n (n ≤ 7), and the oxidation of monolayers yields different sublimable products, notably lactones and dilactonesthus providing clear evidence for a surface-mediated reaction mechanism. After on-top oxidation, roughly 7% of the Coronene monolayer can be sublimed as oxidized derivatives (limited by competing surface reactions, which lead to nondesorbable products). The desorption yield can be raised to 10% by depositing the Coronene monolayer onto preoxidized HOPG. On the basis of our observations and literature results concerning HOPG oxidation, we argue that lactones and dilactones can be generated by the reaction of Coronene adsorbates with epoxy and ether species formed on the graphite support. Our results obtained for the O/Coronene/HOPG model system may be relevant for the mechanism of carbon-based oxidation catalysis in general.
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