Thermal-energy charge transfer, quenching, and association reactions of doubly charged ions in the rare gases

Abstract

A drift-tube mass-spectrometer apparatus has been used to determine thermal-energy (300 K) charge transfer rate coefficients for reactions of the type ${{R}_{a}}^{2+}+{R}_{b}\ensuremath{\rightarrow}{{R}_{a}}^{+}+{{R}_{b}}^{+*}$ and ${{R}_{a}}^{2+}+{R}_{b}\ensuremath{\rightarrow}{{R}_{a}}^{+}+{{R}_{b}}^{2+}+{e}^{\ensuremath{-}}$ (transfer ionization), where $R=\mathrm{H}\mathrm{e},\phantom{\rule{0ex}{0ex}}\mathrm{N}\mathrm{e},\phantom{\rule{0ex}{0ex}}\mathrm{A}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{K}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{X}\mathrm{e}$. Rate coefficients for ions in the low-lying, metastable excited states ($^{1}S$ and $^{1}D$) as well as the ground state ($^{3}P$) have been determined and, in some cases, deexcitation (quenching) coefficients for $^{1}S$ and $^{1}D$ ions have been measured. Reactions with an exoergicity $\ensuremath{\Delta}E\ensuremath{\sim}4$ eV are found to be fast, approaching the limiting Langevin rate, while for $\ensuremath{\Delta}E<2 \mathrm{and} >7$ eV the rates fall off dramatically, in some cases dropping to the radiative value (${\mathrm{\ensuremath{\sim}}10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{3}$/sec). The equilibrium constant for the three-body association reaction ${\mathrm{Xe}}^{2+}$ + 2 Ne\ensuremath{\rightleftarrows}${(\mathrm{Xe}\mathrm{Ne})}^{2+}$ + Ne has been determined at 300 K.