In situ reflection absorption magnetic circular dichroism: methodology and preliminary results

Abstract

The development of a host of new in situ spectroscopic techniques over the past decade has made a major impact towards achieving a better understanding of elementary processes at electrode-electrolyte interfaces [l]. Because of their high sensitivity, in situ optical methods in the UV-visible region lend themselves to this type of application and, as such, have been widely used for monitoring a variety of surface reactions. These include the adsorption of ions, atoms and molecules on electrode surfaces, as well as the changes in the electronic structure of metals, and particularly single crystal surfaces, induced by the externally applied potential [2]. Increased sensitivity to changes in the physicochemical properties of the interface may be attained by monitoring modifications in the polarization state of light reflected off electrode surfaces. This is best illustrated by the widespread application of ellipsometric techniques to the general field of electrochemistry [3]. Methods that rely on the analysis of the behavior of right and left circularly polarized light at electrochemical interfaces, however, have received far less attention. This may be attributed in part to the rather restricted class of molecules of electrochemical interest which possess chiral centers. Optical activity can be induced, however, by applying an external magnetic field, a phenomenon that constitutes the basis of a well developed spectroscopic method known as magnetic circular dichroism, MCD [4]. In direct analogy with the more conventional circular dichroism, MCD measures the differences in the absorption coefficient obtained with right and left circularly polarized light of a species either in solution or in the solid state. This technique can provide unique information that can be complementary to that derived from other