The isotopic resonance hypothesis (IsoRes) postulates that certain isotopic compositions of chemical elements affect kinetics of chemical reactions involving molecules built of these elements. The isotopic compositions for which this effect is predicted are called resonance isotopic compositions.
Fundamentally, the IsoRes hypothesis relies on a postulate that less complex systems exhibit faster kinetics than equivalent but more complex systems. Furthermore, system's complexity is affected by its symmetry (more symmetric systems are simpler), and symmetry (in general meaning) of reactants may be affected by their isotopic composition.
The term “resonance” relates to the use of this term in nuclear physics, where peaks in the dependence of a reaction cross section upon energy are called “resonances”. Similarly, a sharp increase (or decrease) in the reaction kinetics as a function of the average isotopic mass of a certain element is called here a resonance.