THERMOCHEMICAL DETERMINATIONS BY THE KINETIC METHOD

Under appropriate conditions, the kinetics of the dissociation of mole cular cluster ions can yield relative, but quantitative, thermochemica l information on the constituent species. Cluster ions bound via proto ns, electrons, or other atomic or polyatomic anions or cations can be isolated and their dissociations followed in a tandem mass spectrometr y experiment. The isolated, internally excited, proton-bound dimers of organic molecules dissociate competitively to yield the individual pr otonated monomers to a relative extent which is quantitatively related to the difference in proton affinities of the two monomers. This revi ew (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 ac idity and basicity, and when possible compares the data it yields to t hose derived from conventional ion/molecule reaction studies; (iv) sum marizes emerging applications of the method to measurements on biologi cal compounds, including amino acids, peptides, and nucleosides; (v) d escribes applications of the kinetic method to the measurement of othe r thermochemical properties, including electron, metal ion, and haloge n cation affinities; (vi) notes some new areas of application of the k inetic method, including its use to investigate steric, electronic, an d structural effects in cluster ions, and to measure proton affinities of free radicals; and (vii) covers recent experimental studies that c orroborate and refine the underlying theoretical treatment of the meth od. Future applications, including the use of molecular clusters as th ermometer ions and the estimation of thermochemical properties of shor t-lived or otherwise inaccessible chemical entities, are also suggeste d. (C) 1995 John Wiley and Sons, Inc.