Results of a study of inelastic ion scattering on a polycrystalline Mg
surface during the initial stages of oxidation is presented. This is
supplemented by AES measurements and work function determination using
autoionising state electron spectroscopy. The AES oxygen peak intensi
ty rises rapidly for exposures below 2 L and saturation is almost reac
hed at 5 L. A strong decrease in the work function is found below 2 L.
In this region a dramatic fall in the probability of excited state pr
oduction in the scattered flux is observed and found to be state selec
tive. These relative changes are indicative of changes in electron tra
nsfer rates, which are thus determined as a function of exposure. The
general decrease of the intensity of excited states is interpreted as
due to screening of Mg atoms by the adsorbate starting from small cove
rages, below 2 L. The assignment of excited sputtered Mg states is dis
cussed.