Mass Spectrometer Analysis Studies of Cesium Discharges

Abstract

Ion sampling measurements have been made on cesium plasmas for normalized pressures from 10⁻⁴ to 1 Torr using dc as well as rf excitation. For dc discharges, sampling was undertaken through both the anode and the cathode. The major cesium ions observed were Cs⁺, ${\mathrm{Cs}}_2^{+}$ , and ${\mathrm{Cs}}_3^{+}$ . Measurements were made of the ion current ratios, $\mathrm{I(}{\mathrm{Cs}}_2^{+}\mathrm{)/I(}{\mathrm{Cs}}^{+})$ and $\mathrm{I(}{\mathrm{Cs}}_3^{+}\mathrm{)/I(}{\mathrm{Cs}}_2^{+})$ as a function of normalized pressure. Comparison of the observed dependencies with those predicted using steady‐state kinetics provides estimates of the rate coefficients of the following reactions: $$\begin{array}{cc}\mathrm{Cs}\mathrm{**+}\mathrm{Cs}\to {\displaystyle {lim}^{K_2}}{\mathrm{Cs}}_2^{+}\mathrm{+e,}& K_2{\text{τ≃2×10}}^{\text{−15}}{\mathrm{\hspace{0.17em}cm}}^3,\\ {\mathrm{Cs}}^{+}\text{+2}\mathrm{Cs}\to {\displaystyle {lim}^{\beta }}{\mathrm{Cs}}_2^{+}+\mathrm{Cs},& {\text{β≃1.5×10}}^{\text{−29}}{\mathrm{\hspace{0.17em}cm}}^6\mathrm{/sec,}\\ {\mathrm{Cs}}_2^{+}\text{+2}\mathrm{Cs}\to {\displaystyle {lim}^{\gamma }}{\mathrm{Cs}}_3^{+}+\mathrm{Cs},& {\text{γ≃3×10}}^{\text{−29}}{\mathrm{\hspace{0.17em}cm}}^6\mathrm{/sec,\hspace{0.17em}and}\\ {\mathrm{Cs}}_3^{+}\mathrm{+e\to }{\displaystyle {lim}^{{\alpha }_3}}3\mathrm{Cs}{\mathrm{+h\nu }}_3,& {\alpha }_3{\text{≃2×10}}^{\text{−8}}\hspace{0.17em}{\mathrm{cm}}^3/\sec \end{array}$$ .