Adsorption of Carbon Monoxide on a Tungsten (110) Surface

Abstract

A clean (110) tungstensurface can adsorb CO molecules in two different ways. Those striking bare surface have high sticking probability and are held firmly with possible rearrangement of the surface‐metal atoms. Molecules striking an already covered surface have a somewhat lower sticking probability and are held more weakly. Temperatures producing rapid desorption of the two components are 450° and 1100°K. The maximum coverage in the first layer is not pressure dependent. In the second layer the maximum coverage is about 0.8 of the first‐layer coverage at 10−7 torr but decreases slightly at lower CO pressures. The structure of the first layer, as found by LEED observations, is very disorganized unless the crystal is heated; but a well‐ordered structure is produced by heating at 925°K and poorer order by heating at lower temperatures. The ordered surface mesh is C(9×5). The detailed structure has not been determined. The intensities of various diffraction beams from a clean surface change in very complicated ways when the primary beam energy is altered; the variation with energy is much simpler when CO is adsorbed on the surface. A suggested distortion of the clean surface that accounts for these facts is presented.