Translational energy dependence of cross sections for reactions of OH-( H 2 0 ) n with CO 2 and 50 2

A tandem mass spectrometer has been used to measure cross sections for reactions of the solvated negative ions OH-(H20)n' where O.;;;n .;;;3, with the neutral molecules CO2 and S02 over the range of reactant translational energy 0.15-25.0 e V (LAB). The reactions observed include solvent switching, collisional dissociation, and charge transfer. The exoergic solvent switching reactions are very rapid, having cross sections which exceed a hundred square Angstroms at low energies. These cross sections decrease approximately as (energy) O.S up to 1 e V and then decrease much more rapidly at higher collision energies. Estimates of bond dissociation energies for the cluster ions are derived from the measured translational energy thresholds for the endothermic collisional dissociation reactions.