Charge-Exchange Collisions Between Hydrogen Ions and Cesium Vapor in the Energy Range 0.5-20 keV

Charge-exchange collisions have been studied when H⁺ ions and ground state H⁰ atoms are incident on Cs vapor. Measurements of the positive, neutral, and negative beam components after passage through the target were made as a function of the Cs target thickness at several energies between 0.5 and 20 keV. All three beam components were found to approach charge equilibrium monotonically. The maximum H^- equilibrium yield is (21 ±{} 4)%, which occurs at an H⁺ energy of 0.75 keV. The H^- yield decreases with increasing energy, and is 0.4% at 20 keV. At energies below 4 keV the H⁺ equilibrium yield is very small compared with the yield of H⁰ and H^-. For energies greater than 10 kev the H^- equilibrium yield is very small compared with the yield of H⁰ and H⁺. The cross sections σ₊₀, σ_+-, σ₀₊, and σ_0- were measured. The subscripts + and - refer to the H⁺ and H^- ions, 0 as an initial subscript refers to a ground-state H⁰ atom, and 0 as a final subscript refers to an H⁰ atom in the particular states produced. The cross section σ₊₀ decreases with increasing energy, and ranges from (9.4 ±{} 2.0) ×{} 10^-15 cm² at 1 keV to (7.5 ±{} 1.1) ×{} 10^-16 cm² at 15 keV. The cross section σ_+- decreases with increasing energy in the range 2-15 keV, and has the value (2.1 ±{} 0.6) ×{} 10^-17 cm² at 5 keV. The cross section σ₀₊ increases with increasing energy, having the value (1.2 ±{} 0.2) ×{} 10^-17 cm² at 2 keV, and (1.74 ±{} 0.26) ×{} 10^-16 cm² at 15 keV. The cross section σ_0- decreases with increasing energy, having the value (1.5 ±{} 0.3) ×{} 10^-16 cm² at 2 keV and (1.4 ±{} 0.2) ×{} 10^-17 cm² at 15 keV.