Reply to the 'Comment on: 'Nascent Product Excitations in Unimolecular Reactions: The Separate Statistical Ensembles Method''

摘要

In Troe's Comment, he points out that the SSE model, which fits our NCNO results very well, cannot provide accurate rate coefficients and does not fit the nascent state distributions for other unimolecular reactions such as H2O2 and CF3CN, which have been fit by SACM. He also discusses the most economical way to represent product distributions, and suggests the SACM is the best choice. It is important to not lose sight of the fact that statistical theories of unimolecular reactions are used for the rather practical reason that they are easy to implement and work well. There can be no first principles justification of their accuracy, regardless of how many parameters are used to fit experiments and calculations, and the parameters used in statistical models should not be assigned a physical significance that goes beyond their use. At present, it is not feasible to perform quantum scattering calculations on accurate potential energy surfaces (PES's), and even classical trajectories on accurate PES's are rare. Therefore, if the scientific community is to make useful extrapolations and predictions, it must presently rely on models which are mainly statistical. By their nature, such models rely on comparisons with experimental results, for carefully chosen processes which provide tests of the different features of the models. With this philosophy in mind, the authors they have chosen to study the unimolecular reaction of NCNO, and they believe that this system provides the best set of experimental results reported to date concerning nascent product excitations.