The physical and mathematical basics of electron charge transfer absent chemical bonds leading to pseudocapacitance was developed by Rudolph A. Marcus. Marcus Theory explains the rates of electron transfer reactions—the rate at which an electron can move from one chemical species to another. It was originally formulated to address outer sphere electron transfer reactions, in which two chemical species change only in their charge, with an electron jumping. For redox reactions without making or breaking bonds, Marcus theory takes the place of Henry Eyring's transition state theory which was derived for reactions with structural changes. Marcus received the Nobel Prize in Chemistry in 1992 for this theory.