Resonant double photoionization of lithium studied with medium energy resolution

Abstract

We have measured the relative photoionization cross section for the formation of ${\mathrm{Li}}^{2+}$ ions between 148 and $161\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ photon energy with higher photon-energy resolution than in previous ${\mathrm{Li}}^{2+}$ studies. This energy region is characterized by double and triple excitations that lead to strong enhancements in the ${\mathrm{Li}}^{2+}$ cross section. As a result, the double-to-single photoionization ratio shows a dramatic resonance structure not seen before. We have determined the resonance positions and widths using Fano-profile fits to the ${\mathrm{Li}}^{2+}$ data and compare them to previously published values and a calculated ${\mathrm{Li}}^{2+}$ cross-section curve.