Under appropriate conditions, the kinetics of the dissociation of molecular cluster ions can yield relative, but quantitative, thermochemical information on the constituent species. Cluster ions bound via protons, electrons, or other atomic or polyatomic anions or cations can be isolated and their dissociations followed in a tandem mass spectrometry experiment. The isolated, internally excited, proton-bound dimers of organic molecules dissociate competitively to yield the individual protonated monomers to a relative extent which is quantitatively related to the difference in proton affinities of the two monomers. This review (i) describes the origins of the kinetic method; (ii) explores its theoretical basis and the validity of the approximations that underlie it: (iii) surveys the use of the kinetic method to study gas-phase acidity and basicity, and when possible compares the data it yields to those derived from conventional ion/molecule reaction studies; (iv) summarizes emerging applications of the method to measurements on biological compounds, including amino acids, peptides, and nucleosides; (v) describes applications of the kinetic method to the measurement of other thermochemical properties, including electron, metal ion, and halogen cation affinities; (vi) notes some new areas of application of the kinetic method, including its use to investigate steric, electronic, and structural effects in cluster ions, and to measure proton affinities of free radicals; and (vii) covers recent experimental studies that corroborate and refine the underlying theoretical treatment of the method. Future applications, including the use of molecular clusters as thermometer ions and the estimation of thermochemical properties of short-lived or otherwise inaccessible chemical entities, are also suggested.
|Journal||Mass Spectrometry Reviews|
|Publication status||Published - 1994|
|MoE publication type||A2 Review article in a scientific journal|