Ionization of sodium and potassium vapour by 20-100 keV H+and He+ions

A modulated crossed-beam technique has been used to study the ionization of potassium and sodium vapour by 20-100 keV H + and He + ions. Absolute cross sections sigma e for electron production have been determined from the gross yield of electrons. Mass spectrometric measurements of the relative abundance of secondary ion species, together with measurements (in a subsidiary experiment) of the total one-electron capture cross section sigma 10 have been used to determine cross sections for Na + , K + , and K 2+ formation. Proton impact ionization cross sections are shown to be in generally poor accord with theoretical estimates based on both the classical impulse and Born approximations.