Electron-temperature dependence of recombination of electrons with H3O+·(H2O)n-series ions

Abstract

A microwave-afterglow mass-spectrometer apparatus has been used to determine the dependence on electron temperature $T_e$ of the recombination coefficients $\alpha$ of the hydronium-series ions ${\mathrm{H}}_3{\mathrm{O}}^{+}·{\left({\mathrm{H}}_2\mathrm{O}\right)}_n$. For $n=1-3\mathrm{}$, we find $\alpha \left({37}^{+}\right)=(2.5\mathrm{}\pm 0.5)\times {10}^{-6\mathrm{}} {\left[\frac{300}{T_e} \right(\mathrm{K}\left)\right]}^{0.08}$, $\alpha \left({55}^{+}\right)=(3.0\mathrm{}\pm 0.6)\times {10}^{-6\mathrm{}} {\left[\frac{300}{T_e} \right(\mathrm{K}\left)\right]}^{0.08}$, and $\alpha \left({73}^{+}\right)=(3.6\mathrm{}\pm 0.7)\times {10}^{-6\mathrm{}} {\left[\frac{300}{T_e} \right(\mathrm{K}\left)\right]}^{0.00}$ ${\mathrm{cm}}^3$/sec over the range $300-400 \mathrm{K}\le T_e\le 6000-8000 \mathrm{K}$ and $T_{\mathrm{gas}}=T_{+}=300-400\mathrm{}$ K. For $n=4\mathrm{} \mathrm{and} 5$, $\alpha \left({91}^{+}\right)\simeq \alpha \left({109}^{+}\right)\sim 5\times {10}^{-6\mathrm{}}$ ${\mathrm{cm}}^3$/sec, with no apparent dependence on $T_e$. These results for the higher hydrates differ somewhat from those obtained by Leu, Biondi, and Johnsen. The very weak dependence of $\alpha$ on $T_e$ is quite similar to the behavior noted for the $\mathrm{N}{{\mathrm{H}}_4}^{+}·{\left(\mathrm{N}{\mathrm{H}}_3\right)}_n$ cluster ions.