Transition-state Theory and Minimum Density of States

NOcrocanonical IVaa lioii-slale Theory and Mfinimnai Density of Stales.—Several authors have discussed the application of microcanonical transition-state theory, together with die use of the ariterion of minimum state density. This can be dealt with concisely in terms of the adiabatic diannel model (the basic ideas of the following discussion have been givm also by Eliason and Hirschfelder).  

The index min stands for minimum value of fV for q q . Togeth with equation (47), one has then the int esting sequence of inequalities  

These expressions hold, of course, only if one evaluates all quantities using the same potential surface. Equation (51) is a minimum number of locaity open cluinneb criterion (equivalent to counting a minimum number of states of the activated complex ). This follows logically from the adiabatic channd model. A related mininum density of states criterion has been proposed by Bunker and I ttengill on the basis of a comparison with classical trajectory results. In our notation diis corresponds to an evaluation of q by  

Apart from the original use of equation (53) by Bunker and Pattengill, there have been recent applications to several systems. It has been applied to kinetics of dissociation of ethane and recombination of methyl radicals. 

Still another version of the minimum density of states riterion has been used in calculations on NO2 dissociation.The value of q was detennined from equation (53), but the number of states of the activated complex was taken to be W = iV[E - instead of W = W E — It has been sug- 

---