A measurement of the cross section for electron impact ionisation of Al+

Abstract

The crossed ion and electron beams technique has been used to make an absolute measurement of the cross section for the ionisation process e+Al+ to 2e+Al2+ at electron energies ranging from below threshold up to 750 eV. The compounded random and systematic errors are estimated to be about +or-5% at energies in excess of about 25 eV. The cross section for the ground-state ion is determined from the measured data using a small correction that allows for the presence of about 9% of metastable ions in the Al+ beam. Comparison of the present data with the predictions of Lotz shows that the latter work appreciably overestimates the ground-state cross section at energies above 35 eV. The scaled Born prediction of McGuire is in closer agreement but it also exceeds the measured cross section above 35 eV. The shape of the Coulomb-Born-exchange cross section of Moores is in fair agreement but the magnitude is lower than the present data.