Unimolecular reaction rate theory for highly flexible transition states: use of conventional coordinates

An alternative method for implementing RRKM theory for unimolecular reactions with highly flexible transition states is described using conventional coordinates. The number of available states for motion in the transition state state N_(EJ) is determined via an appropriate average over the absolute space orientations and body-fixed momenta of the two fragments. The results of calculations of N_(EJ) for the C_2H_6 → 2CH_3 reaction (or alternatively for the corresponding recombination reaction) obtained from the present expression are shown to be equivalent numerically to those obtained previously by Wardlaw and Marcus