ADSORPTION AND DECOMPOSITION OF CF3I ON CLEAN AND IODINE-PRECOVERED AG(111)

To enhance our understanding of the thermal interactions of fluorocarb ons with transition-metal surfaces, CF3I was adsorbed on clean and iod ine-precovered Ag(111) and studied by temperature-programmed desorptio n (TPD), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelec tron spectroscopy (UPS), and Auger electron spectroscopy (AES). On cle an Ag(111) at 105 K, dissociative adsorption dominates at low coverage s and molecular adsorption at high coverages. Dissociation involves C- I bond cleavage; there is no evidence for C-F cleavage, even during TP D. While multilayer desorption peaks near 118 K, chemisorbed CF3I deso rbs in a sharp peak at 126 K with a high-temperature shoulder near 145 K. The only other detectable desorption products are CF3(g) and I(g), which desorb at 300 and 830 K, respectively. In the presence of low c overages of I(a), less CF3 and more CF3I desorbs. When the surface I/A g ratio is 0.33 (square-root 3 X square-root 3 R30-degrees structure), the dissociation channel is completely suppressed. The influence of a tomic iodine is discussed in terms of combined electronic and site blo cking effects.