AN ELECTRON-STIMULATED DESORPTION ION ANGULAR-DISTRIBUTION AND LOW-ENERGY-ELECTRON DIFFRACTION INVESTIGATION OF CF3I ON RU(001)

We have investigated the structures of CF3I, and its dissociation prod ucts, adsorbed an Ru(001) using low-energy electron diffraction and el ectron-stimulated desorption ion angular distribution (ESDIAD). Atomic iodine forms (root 3x root 3)R30 degrees islands even at very low cov erages. At 70% of saturation and above, a (2x2) superstructure forms w hich we attribute to a p(2x2) unit cell with one CF3 group and one iod ine atom. ESDIAD images show F+ desorbing at normal emission and in th ree hexagonal patterns. The normal emission is attributed to a tilted configuration of CF3(ad) in which one C-F bond is oriented perpendicul ar to the surface. A small hexagon is attributed to F(ad) on step edge s. A large hexagon at low coverages may arise from isolated CF3(ad) sp ecies possessing C-3v symmetry. And finally, an intermediate hexagon i s attributed to perturbation of the CF3(ad) orientation by molecular f ragments which result from electron irradiation of physisorbed CF3I.