Structure and Stability of a High-Coverage (1 x 1) Oxygen Phase on Ru(0001).

The formation of chemisorbed O phases on Ru(0001) by exposure to O{sub 2} at low pressures is apparently limited to coverages {Theta}{le}0.5. Using low-energy electron diffraction and density-functional theory we show that this restriction is caused by kinetic hindering and that a dense O overlayer ({Theta}=1) can be formed with a (1{times}1) periodicity. The structural and energetic properties of this new adsorbate phase are analyzed and discussed in view of attempts to bridge the so-called {open_quote}{open_quote}pressure gap{close_quote}{close_quote} in heterogeneous catalysis. It is argued that the identified system actuates the unusually high rate of oxidizing reactions at Ru surfaces under high oxygen pressure conditions. {copyright} {ital 1996 The American Physical Society.}