Statistical modeling of collision-induced dissociation thresholds

Abstract

Analysis of the energy dependence of the cross sections for collision-induced dissociation reactions has permitted the determination of quantitative thermodynamic information for a variety of ionic clusters. As such clusters become larger, the rate at which the decomposition occurs becomes comparable to the instrumental time available for observing the reaction. A method for incorporating statistical theories for energy-dependent unimolecular decomposition in this threshold analysis is reviewed and updated. The revision relies on the fact that for most ionic clusters, the transition state is a loose association of the products that can be located at the centrifugal barrier. This permits a straightforward estimation of the molecular parameters needed in statistical theories for the transition state. Further, we also discuss several treatments of the adiabatic rotations of the dissociating cluster. The various models developed here and previously are compared and used to analyze a series of data for Li+(ROH) complexes, where ROH=methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, s-butanol, and t-butanol. The trends in the bond energies derived by these various models are compared and their accuracy evaluated by comparison with relative values determined by equilibrium methods.