Electron-Bombardment Desorption: Carbon Monoxide Adsorbed on Tungsten

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Abstract
Experiments are described in which the surface properties of an electron-bombarded tungsten (211) surface are studied by the technique of surface mass spectrometry. In most of the work the tungsten ribbon was in a controlled carbon monoxide atmosphere at a pressure between 10−9 and 10−6 torr. Electrons bombarding this surface release an O+ ion current which has two distinctly separate components coming from different molecular sorption states. The smaller of these components has been identified as direct desorption from the α-phase carbon monoxide. The other was observed to depend in a complex manner upon both the sorption of gas on the surface and the prior history of electron bombardment. These results can only be explained fully by assuming that the electron bombardment produces an intermediate adsorbed state having a large cross section for O+ ion desorption under subsequent electron bombardment. This so-called “intermediate” state is stable always building up to the same equilibrium density under prolonged electron bombardment.