Harpooning in scattering of O2+ from Ag(111): dependence on initial beam energy and direction

Harpooning transitions have been observed in collisions of O2+ at energies Ei=100-400 eV from Ag(111) leading to O- and O2- ions. Specular scattering is predominant. The degree of dissociation of the negative ions observed seems to scale with En=Eicos2(θi) and depends on the azimuthal angle. It is argued that collision induced dissociation is the major cause of the dissociation observed. (author)