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

The formation of chemisorbed O phases on Ru(0001) by exposure to ${\mathrm{O}}_2$ 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 $(\Theta =1\mathrm{})$ 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 “pressure gap” 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.