The RRK Theory was the first in a long series of attempts to calculate the k rate constant tin a uni-molecular reaction. RRK theory is based on two assumptions: (1) the “strong collision assumption”, and (2) the “free energy migration assumption”. The weakest part of the RRK theory of uni-molecular reactions is the free-energy migration assumption. The free energy migrations assumption treats vibrational energy as being re-allocated randomly in a molecule with an unknown frequency.

The free energy migration assumption does not have to be invoked if the dynamics of the system are explicitly accounted for. In this paper, we show how use of explicit dynamics can be used to rid the RRK theory of its least valid approximation, the free energy migration assumption.