A measurement of the cross section for ionization of Li+to Li2+by electron impact

A new apparatus, based on the crossed-beam principle, has been used to measure the cross section of Li + in the reaction Li + + e -> Li 2+ + 2e for electron energies up to 1000 eV. The cross section reaches a maximum value 4 0 × 10 -18 cm 2 for electrons of 350 eV energy. The maximum total errors of the measurements are assessed to be ± 25% near threshold and ± 10% at higher electron energies. Within these limits the results agree with the measurements on Li + by Lineberger, Hooper and McDaniel in 1966. The present measurements also agree very closely with cross sections for the ionization of neutral helium measured by Smith in 1930 when the latter are multiplied by the classical scaling factor (χ 2 /χ 1 ) 2 . Here χ 1 and χ 2 are the ionization energies of Li + and He respectively