| Abstract
| - High-level ab initio calculations were carried out on a series of K+·X cluster ions (X = O, O2, N2, CO2, H2O)and X·K+·Y ions. Rice−Ramsberger−Kassel−Markus theory was then used to estimate the rate coefficientsfor a series of recombination and ligand-switching reactions that govern the ion−molecule chemistry of K+in the upper mesosphere and lower thermosphere. These rate coefficients were then included in an atmosphericmodel of potassium chemistry. The important result is that K+ forms weakly bound clusters with N2, O2, andO (the major atmospheric species), with binding energies between 10 and 22 kJ mol-1. Even under atmosphericconditions (200 K and 10-3 Torr), these cluster dissociate in less than 1 s. This prevents the formation byligand-switching of the more stable CO2 and H2O clusters, which could then undergo dissociative recombinationwith electrons to produce K. The result is that K+ ions have a much longer lifetime against neutralization inthe upper atmosphere than other metallic ions such as Na+ and Fe+.
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