THE ADSORPTION OF ETHENE ON CLEAN AND CHLORINE-PRECOVERED AG(100)

RAIRS, in conjunction with LEED and electron spectroscopies, has been used to characterise both the low-temperature adsorption of ethene on the Ag(100) surface and the influence of preadsorbed chlorine on this adsorption. On the clean surface, ethene is found to be weakly pi-bond ed at all coverages with dynamic pressures being required to saturate the monolayer adsorption state at 100 K. At low coverages, the molecul e lies parallel to the surface plane, but further adsorption induces a reorientation involving rotation about the C-C axis. The influence of preadsorbed chlorine depends critically on the Cl coverage. At low co verage values adsorption is enhanced and LEED shows the presence of or dered ethene-chlorine structures, although no substantial re-hybridisa tion of the ethene is induced. At high Cl coverage a progressive passi vation of the surface is produced.