Elastic and Inelastic Scattering of Low-Velocity H— Ions in Hydrogen

An improved apparatus for the production of beams of negative ions and the measurement of the elastic and inelastic scattering of negative ions in gases at low pressures in briefly described. The measured cross-sections are given for the scattering of 4—400 ev H— ions in hydrogen. In the range 4—40 ev (1.1—1.8 A) the interaction potential derived from the elastic scattering is V (ev) = —4.64×10—32/r4 (r in cm) which is close to the theoretical polarization interaction. The inelastic scattering is presumed to be due to electron detachment. The inelastic cross section increases from 1 cm—1 at 7 ev to 8.7 cm—1 at 395 ev. Above 75 ev the measured elastic cross section increases with increasing ion energy. This is attributed to the appearance of inelastic collisions which result in electronic excitation of the hydrogen molecules.