Adsorption of O-2 on Si(111) 7 X 7 at 30 K is studied by UV photoelect
ron spectroscopy and compared to previous results at 300 K. This demon
strates the existence of two distinct metastable states of O-2 adsorbe
d on Si(111)7 X 7. Furthermore, it is shown that the initial relative
population of these metastable states depends on both the temperature
and the O-2 coverage.