Reaction Rates of Uranium Ions and Atoms with O2 and N2

Abstract

A drift mobility‐tube‐mass‐spectrometer apparatus has been used to study the ion‐molecule reaction, ${\mathrm{U}}^{+}+{\mathrm{O}}_2\to {\mathrm{UO}}^{+}+\mathrm{O}$ , from thermal (300°K) energy to ∼5 eV ion mean energy. At 300°K, the reaction rate is ${\text{(8.5, −1, +4) × 10}}^{\text{−10}}\hspace{0.17em}{\mathrm{cm}}^3/\sec$ and falls slowly with increasing ion energy to ${\text{∼ 7 × 10}}^{\text{−10}}\hspace{0.17em}{\mathrm{cm}}^3/\sec$ at 5 eV. The corresponding reaction of U⁺+N₂ is endothermic and not detected to occur up to ∼5 eV ion energy. Chemi‐ionization of uranium by the association reaction $\mathrm{U}+{\mathrm{O}}_2\to {\mathrm{UO}}_2^{+}\mathrm{+e}$ is detected. An estimate of the total reaction rate for U+O₂, including the oxidation branch to produce UO+O, yields a value ${\text{∼ 2 × 10}}^{\text{−12}}\hspace{0.17em}{\mathrm{cm}}^3/\sec$ at 300°K. Implications of these studies for ion cloud generation in the ionosphere are discussed.