ELECTROSORPTION VALENCY AND PARTIAL CHARGE-TRANSFER IN HALIDE AND SULFIDE ADSORPTION ON AG(111)

The electrosorption valency l(B) of an adsorbed species is usually obt ained from the slope of plots of the charge density on the metal again st the surface concentration of the given species, at constant applied potential. Herein, two alternative procedures for the estimate of l(B ) are proposed and applied to the formation of ordered overlayers of c hloride, bromide, iodide, and sulfide on Ag(111). One of these procedu res applies to strongly adsorbing anions, whose incipient adsorption t urns out to be diffusion controlled under limiting conditions when ste pping from a potential negative enough to exclude their specific adsor ption. This procedure allows l(B) to be estimated as a function of the applied potential. Partial charge-transfer coefficients lambda estima ted from l(B) values on the basis of some modelistic assumptions decre ase in the order sulfide approximate to iodide > bromide > chloride, n amely in the order of increasing Pauling's electronegativity. Some dir ect procedures for the estimate of lambda, which avoid the intermediat e estimate of l(B), are shown to lead to erroneous results.