Coadsorption of anions and water molecule during underpotential depositionof Cu and Ph on the Au (111) electrode surface

Coadsorption of water and anions and IR background shift were observed duri ng the underpotential deposition of Cu on Au (111)in H2SO4 and in HClO4 sol utions using attenuated total reflection-infrared spectroscopy. Phase trans ition of the deposited Cu structures was confirmed by significant frequency shift of the n(S-O) mode from SO43-. Delayed ordering of water to SO43- wa s found. Only LR background shift was observed for the Pb-UPD process due t o an inherently weak interation between Pb and anions. It was rationalized by the effective medium theory assuming a slight change in dielectric const ant of the absorbate layer upon chemisorption. (C) 2001 Elsevier Science B. V. All rights reserved.