Dissociative recombination in xenon: Variation of the total rate coefficient and excited-state production with electron temperature

Abstract

A three-mode microwave afterglow apparatus has been used in conjunction with a high-speed grating spectrometer to study the variation with electron temperature of the recombination coefficient $\alpha \left({{\mathrm{Xe}}_2}^{+}\right)$ and of the Xe* excited states produced by dissociative recombination over the range $300\le T_e\le 8000$ K. At low electron temperatures, 300-700 K, $\alpha \left({{\mathrm{Xe}}_2}^{+}\right)$ varies approximately as $T_e^{-\frac{1}{3}}$, with a smooth transition to a $\sim T_e^{-0.7\mathrm{}}$ variation at higher electron temperatures, 1300-7400 K. At $T_e=T_{+}=T_n=300\mathrm{}$ K, $\alpha \left({{\mathrm{Xe}}_2}^{+}\right)=(2.3\mathrm{}\pm 0.2)\times {10}^{-6\mathrm{}}$ ${\mathrm{cm}}^3$/sec, in agreement with earlier studies at room temperature. At thermal energy (300 K) Xe* excited states up to but not exceeding the energy of the ${\mathrm{Xe}}_2^{+}$ ion in its ground electronic and vibrational state are observed. With microwave heating to $T_e\sim 8000$ K additional, higher-lying Xe* states (up to ∼0.6 eV above the ${\mathrm{Xe}}_2^{+}$ ion ground state) are produced by the dissociative recombination process.