Electron-Temperature Dependence of Electron-Ion Recombination in Neon

Abstract

A 3-mode microwave apparatus is used to determine electron-ion diffusion and recombination rates under conditions such that ${T}_{+}={T}_{\mathrm{gas}}=300$ \ifmmode^\circ\else\textdegree\fi{}K and ${T}_{e}$ is varied from 300 to 11 000\ifmmode^\circ\else\textdegree\fi{}K. A high-$Q$ cavity mode is used to ionize the gas, a second high-Q mode is used to determine the electron density during the afterglow from the change of resonant frequency of the cavity, and a nonresonant waveguide mode is used to apply a constant microwave heating field to the electrons. At ${T}_{e}=300$ \ifmmode^\circ\else\textdegree\fi{}K and $p(\mathrm{Ne})=20$ Torr, a value $\ensuremath{\alpha}(\mathrm{Ne}_{2}^{}{}_{}{}^{+})=(1.7\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec is obtained from analysis of the recombination-controlled electron density decays, using a computer solution of the electron continuity equation to take into account ambipolar diffusion effects. This value is in very good agreement with corrected values obtained by several other investigators. Using the same procedures, a variation of $\ensuremath{\alpha}(\mathrm{Ne}_{2}^{}{}_{}{}^{+})$ as $T_{e}^{}{}_{}{}^{\ensuremath{-}0.43}$ is found to be accurately obeyed over the range $300\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}<~{T}_{e}<~11 000\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}$, suggesting that the initial capture step is rate-limiting in the dissociative recombination process.