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adsorbed 0 or OH". Further SERS experiments using Tc04", an excellent passivating agent, should be a test of this proposal. ConclusionsIn this paper evidence is presented to support the following conclusions:1. (Ag,Cr)-0 and (Ag,Cr)-OH are formed on a Ag electrode after an ORC in a solution of KC1 containing micromolar quantities of Na2Cr207. The (Ag.Cr) adsorption site is similar to the (Ag,Mn) site discussed previously.4a,b 3. The (Ag,Cr)-0 is protonated to form adsorbed hydroxide, (Ag,Cr)-OH, as VSCe is swept cathodically. The addition of 02 gas to the electrolyte deprotonates the hydroxide to form the (Ag,Cr)-0 in a reversible process that involves increasing the interfacial pH.3. The (Ag,Cr)-OH is not further protonated at any obtainable VSCE, indicating that the surface potential for Ag metal with a ~1% Cr impurity level is strongly modified compared to the case when Cr is replace with Mn. This difference in the ability of the surface to form SERS-active H20 suggests that the passivation characteristics of Cr042"-treated metals are related to the H20metal interface.Acknowledgment. The partial support of this research by the Office of Naval Research is gratefully acknowledged.Dr. Bruce Laube and United Technology Corporation made the ISS and SIMS measurements, for which we are appreciative.

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