Collisional detachment cross sections for H⁻and He⁻at high energies

The single- and double-electron-loss cross section for H - and He - ions passing through H 2 , He, N 2 , Ne and Ar gas targets have been studied in the energy range 50-500 keV for H - impact and 100 keV-3 MeV for He - impact. H - and He - ions were formed from H + and He + by charge transfer in a gas cell and the cross sections were determined by the initial-growth method. The experimental cross sections for single-electron loss are compared with theoretical estimates, based upon the semi-empirical impulse approximation of Bates and Walker (1967). A comparison of the experimental results for H - and those for He - impact at equal impact velocities indicates an error of up to 50% in the basic, non-empirical part of the Bates-Walker theory.