STRUCTURE AND STABILITY OF A HIGH-COVERAGE (1X1) OXYGEN PHASE ON RU(0001)

The formation of chemisorbed O phases on Ru(0001) by exposure to O-2 a t low pressures is apparently limited to coverages Theta less than or equal to 0.5. Using low-energy electron diffraction and density-functi onal theory we show that this restriction is caused by kinetic hinderi ng and that a dense O overlayer (Theta = 1) can be formed with a (1 x 1) periodicity. The structural and energetic properties. of this new a dsorbate phase are analyzed and discussed in view of attempts to bridg e the so-called ''pressure gap'' in heterogeneous catalysis. It is arg ued that the identified system actuates the unusually high rate of oxi dizing reactions at Ru surfaces under high oxygen pressure conditions.