Electronic transitions and dissociation in low energy grazing collisions of [formula omitted] with W(110) partially covered by alkali atoms

Abstract

Electron energy spectra from slow (50 eV) O + 2 X 2Π g and a 4Π u molecular ions colliding under grazing incidence with W(110) surfaces are reported. The surface work function was varied by the exposure to alkali (Na, K, Cs) atoms. The electron energy spectra are interpreted in terms of various inter- and intra-atomic Auger processes: For collisions with clean W(110) and alkali coverages below 0.3 monolayers (ML) (in terms of the first completed adlayer at room temperature) Auger capture is observed only. At least for O + 2 X 2 Π g dissociative neutralization does not occur. Beyond this coverage core excited molecular states (molecular Rydberg states), formed by the addition of a 3s σ g electron to the respective ion core, become populated. Their decay manifests itself by Auger deexcitation. In addition we see inter- and intra-atomic Auger processes involving core excited states of atomic oxygen, most probably O ∗( 4S)3s 2. These states originate from the collision induced dissociation of the core excited molecular states. At least for O + 2 a 4Π u the dissociation via core excited molecular states appears to be efficient. From the energy spectra of the O − ions scattered into 90° with respect to the ion beam direction we conclude that under the chosen conditions the O + 2 projectile mainly interacts with the alkali adatoms.