Reflections on electron transfer theory

Abstract

Some of the early history leading to the 1956 The Journal of Chemical Physics article on a theory of electron transfer reactions is described. In the development of electron transfer theory in 1956, the simplicity of the final equation for the free energy barrier, after a lengthy and complex derivation, came to me as a surprise. It was indeed a "Eureka" moment, and I give some of its history here. The theory developed via a rather circuitous route, beginning with a question from a graduate student in a class on statistical mechanics that I taught at Brooklyn Poly. The question was whether a certain model (the Ising model) involving nearest neighbor interactions could be applied to shielded charges along a polymeric chain, a polyelectrolyte. His interest was in applying the theory to experimental data he was obtaining in the laboratory. The answer was yes, and I became interested more generally in the electrostatic properties of polyelectrolytes and in the several seemingly different ways of calculating their electrostatic free energy. To extend my background in electrostatics and treat this topic in a more fundamental way I researched every book on electrostatics/electromagnetic theory in the Brooklyn Poly library and found one that provided physical insight into the various concepts. After writing a pair of articles on polyelectrolytes, I then wondered what to do next. I had long decided that applying a theory I derived in 1952, later known as Rice–Ramsperger–Kassel–Marcus (RRKM) theory, was not a desirable option. There were almost no relevant experimental data on unimolecular reactions or bimolecular recombination reactions at the time. Extensive data, laboratory and computational, for testing the theory were to come later in the 1960s and subsequent decades.

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