1-BROMO-2-CHLOROETHANE ADSORPTION ON CU(111)

Low energy electron diffraction, Auger-electron, and ultraviolet photoemission spectroscopies (UPS) and DELTAphi measurements were used to study the adsorption of 1-bromo-2-chloroethane on Cu(111). Room temperature adsorption led to the formation of a (square-root 3 X square-root 3)R30-degrees structure composed of equal parts chlorine and bromine, the remainder of the molecule returning to the gas phase as ethene. Adsorption at 110 K occured molecularly in a layer by layer mode up to the fourth molecular layer. UPS shows that the first monolayer which is in direct contact with the copper, is oriented and probably in one conformation. On warming, the multilayers desorbed leaving a single layer of 1-bromo-2-chloroethane which had already begun to react with the surface. Physisorbed ethene at 173-183 K has been tentatively identified by UPS as one of the products of this low temperature reaction, the others being Cl(ads) and Br(ads). Further heating desorbed the ethene and left a (square-root 3 x square-root 3)-Cl/Br surface the same as that formed at room temperature. The molecule was also found to undergo a clean electron stimulated reaction, which led to the two chemisorbed halogens and a gaseous product carrying away the carbon, presumably ethene. The behavior of 1-bromo-2-chloroethane is compared with that of 1,2-dichloroethane on the same surface.