Discussion of the Absolute Reaction Rate of Unimolecular Decompositions

In the usual theory of absolute reaction rates it is assumed that the molecules in the activated complex are in statistical equilibrium with the molecules in the initial state. This assumption is not justified in the case of unimolecular decompositions because the molecules in the initial state must gain the energy of activation by a stepwise process, usually by the transfer of quanta of vibrational energy from one normal mode to another. The size of these energy jumps and their frequency inevitably affect the over‐all reaction rate. The problem is considered in considerable detail for a rough idealized mode. In this case, the actual reaction rate should be smaller by a factor of 0.5 to 0.387 than the value computed from the usual theory of absolute rates. A rigorous development would require further development of the original Ramsperger‐Rice‐Kassel treatment.