Abstract
Electron energy spectra from slow (50 eV) CO + 2 molecular ions colliding under grazing incidence (5°) with W(110) surfaces are reported. The surface work function was varied by the exposure to alkali atoms. The electron emission is caused by Auger processes, such as Auger capture for clean W(110) and at moderate alkali coverages, and Auger deexcitation of core excited CO∗ 2 states (formed by the resonant capture of a surface electron by the CO + 2 projectile) at larger alkali coverages (> 0.3 monolayers). A comparison is made with the spectra of the electrons ejected in CO + collisions (also reported here). The CO + and CO + 2 induced spectra are very similar for coverages beyond 0.5 monolayers. This can be explained by assuming that in this coverage range efficient dissociation of the core excited CO 2 states is in competition with the Auger process. The dissociation apparently leads to the formation of excited CO∗ fragments whose Auger deexcitation is observed. O − ions are seen in the spectra of the ions scattered into 90 deg with respect to the beam direction. These could originate from oxygen atoms from the dissociation process which have captured a surface electron thus forming O − ions.
Published Version
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