Measurements of radiative charge-transfer reactions of doubly and singly charged rare-gas ions with rare-gas atoms at thermal energies

Abstract

Radiative charge-transfer coefficients for single-electron transfer between doubly or singly charged noble-gas ions and noble-gas atoms have been determined at thermal energy using a drift-tube mass-spectrometer apparatus. At 300 K, $k({\mathrm{He}}^{2+}+\mathrm{He})=(4.8\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{3}$/sec, with slightly smaller coefficients for the reactions ${\mathrm{Ne}}^{2+}$ + Ne, ${\mathrm{Ar}}^{2+}$ + Ar, ${\mathrm{Kr}}^{2+}$ + Kr, and ${\mathrm{Xe}}^{2+}$ + Xe. Differences in reactivity are found for the different, low-lying $^{1}S$, $^{1}D$, and $^{3}P$ states of the doubly charged ions. A three-body contribution to the radiative process is noted, with rate coefficients ranging between ${10}^{\ensuremath{-}31}$ and ${10}^{\ensuremath{-}30}$ ${\mathrm{cm}}^{6}$/sec at 300 K for the different noble-gas systems. The radiative charge-transfer coefficients for singly ionized ions are somewhat smaller, $k({\mathrm{He}}^{+}+\mathrm{Ne})\ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{3}$/sec and $k({\mathrm{Ne}}^{+}+\mathrm{Ar})\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{3}$/sec at 300 K. The measured value of $k({\mathrm{He}}^{2+}+\mathrm{He})$ is in reasonable agreement with the very recent theoretical calculations of Cohen and Bardsley.