RRKM theory description

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. 

The minimization of the canonical transition state partition function as in Eq. (2.13) is generally termed canonical variational RRKM theory. This approach provides an upper bound to the more proper E/J resolved minimization, but is still commonly employed since it simplifies both the numerical evaluation and the overall physical description. It typically provides a rate coefficient that is only 10 to 20% greater than the E/J resolved result of Eq. (2.11). 

In recent years the semiclassical "statistical theory of RICE, RAMSPERGER, KASSEL, and MARCUS /136/ has made great progress in its development. The computational techniques of this theory provide the possibility of calculating the velocities of unimolecular reactions using suitable, models for the activated complex. This approach is certainly very useful for a correlation of the experimental facts and a description of various aspects of the observed phenomena. The success of such applications of the RRKM-theory does not at all preclude an alternative treatment based on the collision theory of... 

In order to keep the book short, and to minimise its cost, I will not enter into any description of the RRKM theory since it has been dealt... 

The RRKM theory is equivalent to TST, and it allows an arbitrarily detailed description of the TS. PST [12-19], however, assiunes that the colhsional rate coefficient and the rate coefficient k for dissociation of the complex are governed by an orbiting or other type of loose TS, but imlike the usual formulation of RRKM theory, it rigorously conserves angular momentmn. The statistical dissociation rate constant can be calculated from the point of view of the reverse reaction. Again, this procedure is limited to reaction without energy barrier. 

The RRKM (after Rice, Ramsperger, Kassel, and Marcus) theory is, basically, transition-state theory (see, in particular, the description in Section 6.2) applied to a unimolecular reaction. Thus, one focuses on the activated complex... 

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