FULL STRUCTURE DETERMINATION OF AN ALKALI-METAL/CO COADSORPTION PHASE FOR CO(10(1)OVER-BAR-0)-C(2X2)-(K+CO)

A structural analysis of a c(2×2)-(K+CO) coadsorption phase on Co{101̄0} by low-energy electron diffraction has yielded a full picture of the geometry of a model alkali-metal CO coadsorption system. Potassium atoms are located in fourfold hollow sites above second-layer Co atoms, and CO molecules are displaced by 0.5±0.2 from the high-symmetry Co short bridge sites near the center of gravity of the three neighboring K adatoms. The CO causes a substantial increase, by 0.4, in the K-Co nearest-neighbor bond length, and K adatoms are located with their centers above the O atoms in the neighboring CO. This has important implications for the bonding interactions within the adlayer. © 1995 The American Physical Society.