Chemisorption and Oxidation: Oxygen on Tungsten

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Abstract
Oxygen chemisorption and the extent of oxidation on a tungsten ribbon at room temperature were studied by flash desorption using line‐of‐sight detection with a time‐of‐flight mass spectrometer. The only chemical species in the adlayer are oxygen atoms and the monotungstic oxides: WO, WO2, and WO3. These oxides are desorbed with an energy of ∼100 kcal. In agreement with earlier predictions, oxygen desorbs as atoms. Neither molecular oxygen nor polytungstic oxides were ever observed from a ribbon flashed after a room‐temperature exposure to oxygen. However, flowing oxygen on tungsten at surface temperatures > 1400°K does produce the polytungstic oxides. An order‐of‐magnitude estimate of the adlayer composition at room temperature suggests that at saturation there is approximately one monolayer of oxygen atoms in a random configuration with a few tenths of a per cent each of the monotungstic oxides. Consequently, oxidation is not a significant surface process on clean tungsten at room temperature.