Collision Cross Section of Slow Electrons and Ions with Cesium Atoms

Microwave interferometry is adopted to measure the effective-collision cross section for momentum transfer ${\overline{Q}}_m$ of thermal electrons (of mean energies of ∼0.06 to 0.071 eV) with cesium atoms in the afterglow of pure cesium and helium-cesium discharges. The momentum-transfer cross section ${\overline{Q}}_m$ is found to be best represented by $1.61\times {10}^{-10\mathrm{}}{T_e}^{-1\mathrm{}}-9.63\mathrm{}\times {10}^{-12\mathrm{}}{T_e}^{-\frac{1}{2}}+2.03\mathrm{}\times {10}^{-13\mathrm{}}$ ${\mathrm{cm}}^2$ in the temperature range of approximately 450 to 550°K. The energy dependence of the elastic electron-cesium-atom collision probability for momentum transfer is determined to be $P_m=997\mathrm{}{u}^{-1\mathrm{}}-4810\mathrm{}{u}^{-\frac{1}{2}}+7230\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, where $u$ is the energy of the electron volts. This shows a smooth tendency to join Brode's data at higher electron energies. Mobilities of ${\mathrm{Cs}}^{+}$ ions in helium and in cesium have been determined from the helium-cesium mixture experiments in the same temperature range. They are $\mu \left({\mathrm{Cs}}^{+} \mathrm{in}\mathrm{He}\right)=18.5\mathrm{}\pm 0.5$ ${\mathrm{cm}}^2$/V-sec and $\mu \left({\mathrm{Cs}}^{+} \mathrm{in}\mathrm{Cs}\right)=0.4\mathrm{}\pm 0.05$ ${\mathrm{cm}}^2$/V-sec referred to standard gas density (i.e., 2.69×${10}^{19}$/${\mathrm{cm}}^3$).