Marcus theory


![Fig.4. Marcus behaviour in a molecule, which is composed of a biphenyl entity, whose anion (produced by means of pulse radiolysis) acts as a donor, a steroid entity, which is a rigid spacer and different aromatic hydrocarbons (1−3) and quinones (4−8), which are the acceptors.[18]](/uploads/202501/26/Marcusparabel_MillerCloss4240.jpg)
Marcus theory is a theory originally developed by Rudolph A. Marcus, starting in 1956, to explain the rates of electron transfer reactions – the rate at which an electron can move or jump from one chemical species (called the electron donor) to another (called the electron acceptor). It was originally formulated to address outer sphere electron transfer reactions, in which the two chemical species only change in their charge with an electron jumping (e.g. the oxidation of an ion like Fe/Fe), but do not undergo large structural changes. It was extended to include inner sphere electron transfer contributions, in which a change of distances or geometry in the solvation or coordination shells of the two chemical species is taken into account (the Fe-O distances in Fe(H2O) and Fe(H2O) are different).