| Citation | The research of Rudolph A. Marcus has touched upon almost every field of modern theoretical chemical kinetics. He is particularly known for his theories of unimolecular reactions in gases (RRKM theory) and of electron transfer reactions in solution (Marcus theory). In the former he showed how the rate of dissociation or isomerization of a molecule depended on its energy and he related that rate to molecular properties. In this theory earlier statistical ideas were blended with transition state theory.
In the electron transfer theory he calculated the rates of electron transfer reactions in terms of molecular and solvent properties. He showed how the rates of such reactions could be expressed in terms of those of self-exchange reactions and the equilibrium constants of the reactions, and was able to make many other verified predictions.
Both theories have been widely tested experimentally and have become the standard ones in use in their respective fields. They are now textbook material. Marcus extended the electron transfer theory to electron transfer reactions at electrodes - establishing the relation between the two processes - and also extended it to the transfer of other particles such as atoms and protons. The resulting theory provided a framework for treating the free energy barrier to reactions in terms of intrinsic, thermodynamic and work contributions and led to a relation between the rates of these reactions and those of the corresponding self-exchange reactions.
Marcus has made many other seminal contributions to reaction rate theory. His introduction of natural collision coordinates for reactions serves as a basis of "reaction path hamiltonian" methods. In related work he designed new tunnelling paths for chemical reactions. His semiclassical treatment of bound states of anharmonic systems stimulated a resurgence of interest in the field; he showed how classical trajectories could be used to yield a semiclassical quantization for nonseparable anharmonic vibrating systems. His semiclassical theory of inelastic and reactive collisions (in parallel with the work of W.H. Miller), showed how numerically-calculated classical trajectories could be used to provide transition probabilities for the collision and gave insight into quantum-mechanical tunnelling and interference corrections to classical trajectory calculations. |