From the Modeling of Experiments to the Ab Initio Prediction of Rate Constants: Statistical Rate Theory for a Quantitative Understanding of Gas‐Phase Ion Chemistry

Statistical rate theory has long been used for the analysis of gas-phase ion reactions. Traditionally, it has mainly served as a framework for fitting experimental data, often obtained with highly specialized instrumentation, and extracting quantities of interest, such as reaction threshold energies. With the progress in quantum chemical calculations and their ability to provide accurate energy profiles along reaction coordinates, the reliable ab initio prediction of rate constants of gas-phase ion reactions appears to be within reach. Such predictions would be quite valuable, because they enable the direct comparison between the results from theory and standard mass-spectrometric experiments and, thus, aid in the interpretation of the latter. In this review, we seek to answer the question of the extent to which accurate ab initio predictions of gas-phase ion reaction rate constants have become feasible and can be used for routine applications. After covering the basics of statistical rate theory and giving an overview of important programs for rate calculations, we demonstrate and discuss the current state of the field for four different examples: the dissociation of the n-butylbenzene radical cation, the dissociation of benzylpyridinium ions, the unimolecular reactivity of anionic organometallic complexes, and the reactivity of organometallic ions toward proton donors.