A determination of the stabilities of O+2(O2)<i>n</i> and O−2(O2)<i>n</i> with <i>n</i>=1–8 from measurements of the gas-phase ion equilibria

Abstract

The gas-phase equilibria of solvation reactions of O+2 and O−2 ions with O2 were measured with a pulsed electron-beam high-pressure mass spectrometer. van’t Hoff plots of the equilibrium constants lead to the determination of the thermochemical stabilities for O+2(O2)n with n=1–8 and for O−2(O2)n with n=1–7. The fashion of the bonding in the clusters O+2(O2)n and O−2(O2)n changes drastically from covalent to electrostatic one between n=2 and 3, and n=1 and 2, respectively. That is, the first shells formed for these positive and negative cluster ions are O+2(O2)2 and (O2---O2)−. The formation of the second shells, O+2(O2)2(O2)2 and (O2---O2)−(O2)2, are also observed, but they are only slightly more stable than larger clusters toward dissociation.