Rice-Ramsperger-Kassel-Marcus theory, potential energy surfaces

In the statistical description of ununolecular kinetics, known as Rice-Ramsperger-Kassel-Marcus (RRKM) theory [4,7,8], it is assumed that complete IVR occurs on a timescale much shorter than that for the unimolecular reaction [9]. Furdiemiore, to identify states of the system as those for the reactant, a dividing surface [10], called a transition state, is placed at the potential energy barrier region of the potential energy surface. The assumption implicit m RRKM theory is described in the next section. 

Several theories have been developed for the unimolecular reactions. The earliest, proposed by KASSEL, HINSHELWOOD, RICE, and RAMSPERGER /136/, as well as the later theory of SLATER /137/, are based on classical models. The most recent and important theory of MARCUS ans RICE /138/ rests on the semiclassical activated complex theory which makes use of potential energy surfaces. 

---