Single and double photoionization of lithium

The photoion Li²⁺/Li⁺ production cross section ratio of ground-state atomic lithium has been measured for photon energies ranging from 80 to 424 eV. The absolute cross sections for the Li²⁺ and Li⁺ yield are also derived. In this energy region, the Li²⁺/Li⁺ ratio reaches a plateau of about 1.0% before reaching a maximum of about 4.5%, then decreases slowly. Good agreement is found between the measured total photoionization cross sections of lithium and theoretical calculations. The Li²⁺/Li⁺ ratio is also compared to the He²⁺/He⁺ ratio from excited He(1s2s) for photon energies up to 70 eV above threshold. The branching ratio of Li²⁺ to total Li ion production is also compared to the single-ionization cross section of electron impact on Li⁺ ions.