Covalent effects in molecule-surface charge exchange: oxygen on silver(111)

M.C. Zonnevylle, R. Hoffmann, P.J. Hoek, van den, R.A. Santen, van

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Abstract

The formation of neg. charged ions (O2-, O-) in the scattering of oxygen from silver surfaces is difficult to explain with the Brako-Newns scheme. Extended-Hueckel tight-binding calcns. are performed on model Ag(111) slabs, placing O2 adsorbates at various sites and mol. orientations. As the survival probability of a neg. charged ion leaving the surface is detd. by the back-tunneling frequency, the mol. ion survival probably should increase as the O2-Ag interaction decreases, and vice versa. On the other hand, the dissocn. probability will increase with increasing interaction strength. The strength of the O2-Ag interaction can be gaged by the dispersion found in the projected d. of states of the O2 affinity level 1pg. The second moment serves as a measure of relative dispersion, and in addn., can be related to the tunneling frequency. The bridging and hollow sites have the strongest O2-Ag interaction, thus the lowest survival probability of neg. ions and the highest degree of dissocn. The interaction at top sites is much less. These results can be used to explain the higher O-/(O- + O2-) ratio obsd. at more grazing incident beam angles
Original languageEnglish
Pages (from-to)233-257
JournalSurface Science
Volume223
Issue number1-2
DOIs
Publication statusPublished - 1989

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