Introduction

Abstract

It has long been recognized by electrochemists that measurements of electrical currents, voltages, charges, or capacitances do not always provide unequivocal identification of electroactive molecules, i.e., although a diffusion current might be correlated to a particular species, with its peak or half-wave potentials for reduction or oxidation and a diffusion coefficient appropriate to the media, the molecular identity has to be inferred from the measured physical properties of standard systems. In more complex (multilayer) or natural (biochemical or environmental) systems, these properties may not always be resolvable. The ability, therefore, to utilize additional, perhaps more specific, physical characteristics of molecules to monitor electrode processes, in either dynamic or equilibrium conditions, would be immensely valuable. In the past several decades in particular, there have been considerable efforts expended to develop spectroelectrochemical techniques to aid electrochemical research. Molecular properties such as molar absorptivities, vibrational absorption frequencies, and electronic or magnetic resonance frequencies, in addition to the traditional electrical parameters, now are being used routinely to better our understanding of electron transfer reaction pathways and the fundamental molecular states at interfaces.