This chapter discusses In-Situ Electrochemical electron spin resonance spectroscopy (ESR). The existence of radicals as intermediates in a great variety of electrode reactions is well established. Such paramagnetic species may be detected and identified using ESR and so for nearly thirty years electrochemists have used ESR as a method for the investigation of those complex electrode reactions that proceed via radical intermediates. ESR spectra are characterized by three parameters, the g factor, the hyperfine coupling, and the line width. It is these parameters that allow identification of the nature and environment of radicals. The spin-orbit coupling is dependent upon the orientation of the radical within the applied field, making g anisotropic, and thus the position of the observed ESR spectrum is dependent upon the orientation of the radical. Fortunately, for radicals in solution, such as those observed commonly in electrochemical ESR, there is rapid tumbling of the radicals and, effectively, an average g factor is observed. © 1989 Elsevier B.V.
