Negative ion formation and dissociation in scattering of fast O sub 2 and NO from Ag(111) and Pt(111)

Results of scattering of 80--300 eV O{sub 2} and NO from Ag(111) and Pt(111) single crystal surfaces are presented. Molecular negative ion formation occurs on both surfaces. For O{sub 2} scattering around 80 eV for {theta}{sub {ital i}}=70{degree} from Ag(111), the O{sup {minus}}{sub 2} distribution is detected in the specular direction, whereas an off-specular shift towards the surface is observed for scattering from Pt(111). For the Pt(111) surface, a degree of dissociation is observed that is much larger than for the Ag(111) surface. Both observations are consistent with the low dissociative sticking probability for thermal O{sub 2} on Ag(111) reported and the high dissociative sticking probability for thermal O{sub 2} on Pt(111). For NO{sup {minus}}, the degree of dissociation is approximately equal to the degree of dissociation for O{sub 2} at the same Pt(111) surface.