Single and double photoionization of lithium

Abstract

The photoion ${\mathrm{Li}}^{2+}{/\mathrm{L}\mathrm{i}}^{+}$ 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 ${\mathrm{Li}}^{2+}$ and ${\mathrm{Li}}^{+}$ yield are also derived. In this energy region, the ${\mathrm{Li}}^{2+}{/\mathrm{L}\mathrm{i}}^{+}$ 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 ${\mathrm{Li}}^{2+}{/\mathrm{L}\mathrm{i}}^{+}$ ratio is also compared to the ${\mathrm{He}}^{2+}/{\mathrm{He}}^{+}$ ratio from excited $\mathrm{He}(1s2s)$ for photon energies up to 70 eV above threshold. The branching ratio of ${\mathrm{Li}}^{2+}$ to total Li ion production is also compared to the single-ionization cross section of electron impact on ${\mathrm{Li}}^{+}$ ions.