[1][2][3] It was developed by Rice and Ramsperger in 1927[4] and Kassel in 1928[5] (RRK theory[6]) and generalized (into the RRKM theory) in 1952 by Marcus[7] who took the transition state theory developed by Eyring in 1935 into account.
These methods enable the computation of simple estimates of the unimolecular reaction rates from a few characteristics of the potential energy surface.
Assume that the molecule consists of harmonic oscillators, which are connected and can exchange energy with each other.
Assume that A* is an excited molecule: where P stands for product, and A‡ for the critical atomic configuration with the maximum energy E0 along the reaction coordinate.
is the microcanonical transition state theory rate constant,
are the molecular vibrational and external rotational partition functions.