The influence of the potential and polarization conditions on the adsorption kinetics and structure of 2-methyl-5-mercapto-1,3,4-thiadiazole on copper was investigated. The study was carried out by means of cyclic voltammetry, differential capacity, and potentiodynamic electrochemical impedance spectroscopy experiments. The total amount of deposited molecules suggested the formation of a dense organic layer. Several possible molecular adsorption geometries were established by considering some relevant quantum-chemical descriptors. Differentiation between them was performed by a derivation of the layer thickness from its capacitance. The latter was obtained by means of differential capacity and potentiodynamic electrochemical impedance spectroscopy measurements. It was shown that the application of potentiodynamic electrochemical impedance spectroscopy instead of differential capacity approach is beneficial in the case of complex or not purely capacitive systems. The results suggested that the polarization rate influenced significantly the morphology of the formed layers. (c) 2008 Elsevier Ltd. All rights reserved.