Electron Affinities of O2, O3, NO, NO2, NO3 by Endothermic Charge Transfer

Abstract

Lower limits to the electron affinities of the molecules O₂, O₃, NO, and NO₂ have been measured by determining the thresholds for endothermic charge transfer from ${\mathrm{I}}^{-}$ to the corresponding molecules. The technique involves formation of ${\mathrm{I}}^{-}$ by photoion‐pair formation and measurement of the intensity of the product ion as a function of the energy available in the collision. The lower limits obtained are O₂, 0.48 eV; O₃, 1.96 eV; NO, 0.09 eV; and NO₂, 2.04 eV. The threshold for the reaction $${\mathrm{I}}^{-}+{\mathrm{HNO}}_3\to {\mathrm{NO}}_3^{-}+\mathrm{HI}$$ has also been measured, and provides a lower limit to ${\mathrm{\Delta \; H}}_{f_0}^{○}({\mathrm{NO}}_3^{-})$ . When combined with the best current estimate of ${\mathrm{\Delta H}}_{f_0}^{○}({\mathrm{NO}}_3)$ , it yields $\mathrm{E.A.}({\mathrm{NO}}_3\text{)≥2.48\hspace{0.17em}}\mathrm{eV}$ .