Single-Electron Capture and Loss Cross Sections for 2-50-keV Hydrogen Atoms Incident upon Hydrogen and the Inert Gases

The single-electron capture and loss cross sections σ_0,-1 and σ₀₁ for 2-50-keV hydrogen atoms incident upon hydrogen molecules and inert-gas atoms have been measured directly by observing the growth of the fast-collision products (i.e., the fast primary H₁^_⁰ which have changed charge) with the target-gas number density. In H₂, He, Ne, and Ar, the present values of σ_0,-1 and σ₀₁ generally confirm previous measurements, with the notable exception that in H₂ the low-energy values of σ₀₁ are as much as 30% smaller (at 2 keV) than the values of McClure. In Kr and Xe there are no previous measurements of σ_0,-1, while the only previously reported values of σ₀₁ are smaller than the present values by as much as a factor of 3. For a hydrogen-gas target, the present measurements do not show any large subsidiary peaks. The use of an electrostatic field, prior to the collision cell, to quench possible excited states in the primary H₁^_⁰ atom beam is shown to have only a very small effect upon the measured cross sections. Both σ₀₁ and σ_0,-1 are found to increase in value with increasing atomic number for all the inert gases. The low-energy (adiabatic) region is extended down to 2 keV, where it is seen that σ₀₁ rises exponentially with increasing relative velocity of the colliding particles.