Binding energies of alkali metal halide cluster ions: calculated by electrostatic models and measured by the kinetic method

Abstract

Experimental measurement of the binding energy of gaseous alkali halide clusters has been difficult. Recently, Chen and Cooks (J. Mass Spectrom. 1997;32:1258) reported the application of the kinetic method to the measurement of relative bond dissociation energies via competitive fragmentation of mixed ionic clusters [M1XM2]+ generated in a mass spectrometer. In this study the binding energies of various alkali metal halide cluster ions of the form [M1XM2]+ or [X1MX2]− have been calculated using both the rigid-ion model and the polarizable-ion model. The kinetic method was employed to measure the dissociation energies of triatomic cluster ions consisting of different alkali metal ions and halides. Good correlations between the calculated and measured differences in competitive dissociation energies were found for both positively and negatively charged cluster ions. Results further demonstrate the applicability of the kinetic method to measuring the relative bond dissociation energies for ionic compounds. However, it is noted that the kinetic method does not measure the absolute bond dissociation energy between a cation and an anion in the initial state of the tri-atomic cluster ion.