Ionization and charge transfer in fast H⁺-He⁺collisions using an intersecting beam technique

A fast intersecting beam technique has been used to obtain total cross sections sigma (He 2+ ) for He 2+ formation from the combined processes H + +He + to H + +He 2+ +e (ionization) and H + +He + to H+He 2+ (charge transfer) in the centre-of-mass energy range 72-402 keV. At these energies, ionization is believed to provide the main contribution to the measured cross sections which are shown to be in good agreement with cross sections for ionization predicted theoretically by scaling data for H + -H collisions. Values of sigma (He 2+ ) also show the expected tendency to converge to corresponding cross sections for ionization by electron impact at high equivalent velocities.