Electrochemical evidence shows that the oxidation of thiols on mercury is characterized by an extensive adsorption of the oxidized products on the electrode surface, and by the formation of dimeric R-S-Hg-S-R organometallic complexes as the final oxidation products. The orthogonal collocation technique has been used in this work to solve the simplest voltammetric boundary value problem accounting for these observations. The proposed oxidation mechanism includes a following surface dimerization step, and it considers simultaneously the adsorption of the oxidized products. Analytical expressions for the voltammetric wave have been derived when the adsorption strength of the products is either very strong or weak. When the adsorption strength is moderate, numerical results have been used to explore the influence of the dimerization step on the voltammetric shape. Theoretical predictions have been applied to interpret the voltammetric behavior of 3-mercaptopropanol on mercury as a function of the solution pH. Quantitative agreement with the proposed mechanism is only found in the most acid (pH 2) solution, whereas a progressive distortion of the voltammetric waves is observed as the solution pH increases, which is tentatively ascribed to the existence of two low- and high-density surface states of the adsorbed products. (c) 2002 The Electrochemical Society. [DOI: 10.1149/1.1432677] All rights reserved.