Molecular and dissociative adsorption of 1-bromo-2-chloroethane on Cu(111)

The adsorption of 1-bromo-2-chloroethane (BCE) on Cu(lll) in the temperature range 100-300 K has been studied using ultraviolet photoelectron spectroscopy (UPS), work function measurements, low energy electron diffraction, and line of sight temperature programmed desorption (LOSTPD). At 300 K adsorption occurs dissociatively forming ethene (which desorbs) and a (root 3 x root 3)R30 degrees-Br/Cl chemisorbed structure which increases the work function of the surface by 0.75 eV. At 100 K BCE adsorption is molecular, with a decrease in work function of 0.55 eV for the first monolayer. By combining UPS and LOSTPD to study the adsorbed and gas phase products generated by heating the monolayer and multilayer surfaces formed at 100 K, several states of BCE on the Cu(lll) surface have been observed. The A (first layer), B (2nd layer) and C (>2 layers) states correspond to BCE adsorbed prior to any dissociative reaction with the copper surface. Reaction of BCE with the Cu(lll) surface then forms three more states. The A' state isa submonolayer of BCE which has been stabilised by chemisorbed halogen products after partial thermal decomposition (130 K) of a single monolayer of BCE. The A' state undergoes complete dissociation on heating to 150 K. Two molecular BCE desorption states, the B'1 and B'2, are observed on heating multilayers of BCE. They are thought to be due to BCE in the second layer (originally the B state) which is stabilised by chemisorbed halogen products formed by decomposition of the underlying first layer (originally the A state). The possibility of the B' states having a gauche conformation is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.