NEGATIVE-ION FORMATION AND DISSOCIATION IN SCATTERING OF FAST O-2 AND NO FROM AG(111) AND PT(111)

Results of scattering of 80-300 eV O2 and NO from Ag(111) and Pt(111) single crystal surfaces are presented. Molecular negative ion formation occurs on both surfaces. For O2 scattering around 80 eV for theta-i = 70-degrees from Ag(111), the O2- 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 O2 on Ag(111) reported and the high dissociative sticking probability for thermal O2 on Pt(111). For NO-, the degree of dissociation is approximately equal to the degree of dissociation for O2 at the same Pt(111) surface.