Chemisorbed Oxygen Structures on the Rhodium (110) Surface

Abstract

Eight different chemisorbed structures formed by oxygen on the (110) face of Rh are analyzed and discussed. Three are high‐coverage coincidence lattices with rows of oxygen atoms parallel to the close‐packed direction of the substrate and with O/Rh atom ratios of 5/4, 7/8, and 5/6. Two of the structures are formed by oxygen entering the open structure of the surface causing a rearrangement of the Rh atoms to form a combined oxygen and Rh lattice. The necessary Rh atom motions are small (0.7 Å) and the resultant structures form rows of O and Rh atoms, in the ratio of 1:2, normal to the Rh close‐packed rows in a coincidence‐lattice configuration. The remaining three structures are simple low‐coverage structures formed at the end of depletion of the Rh lattice of its oxygen content produced by the original oxygen treatment of the surface. A wide variety of O–O contacts in chemisorbed structures formed on Rh and Pt surfaces is discussed relative to O–O distances observed in three‐dimensional ionic crystals and in covalently bound radicals. The great majority of O–O contacts in the chemisorbed structures fall in the range of O–O ionic contacts. Two fall in the shortest range of covalently bound O–O contacts. When the variation in size with coordination number is considered, it is concluded that the observed O–O contacts fall in the range of, but do not distinguish between, ionic and covalent O‐metal bonds.