Autoionization of foil-excited states in Li i and Li ii

Abstract

We have used the beam-foil interaction mechanism to populate highly excited states in lithium by passing 300-keV ${\mathrm{Li}}^{+}$ ions through 8-\ensuremath{\mu}g/${\mathrm{cm}}^{2}$-thick carbon foils. The energies of the electrons emitted via autoionization were analyzed. By moving the foil along the beam axis, prompt and delayed electrons due to decays of Lii and Liii states were identified. These spectra are interpreted with the help of detailed theoretical calculations. The excitation energies of the $\mathrm{LiI}(1s2{s}^{2})^{2}S^{e}$ and $\mathrm{LiII}(2s2p)^{1,3}P^{o}$ terms were determined to 0.5% accuracy. We have observed decays of doubly excited Liii states above the $n=2$ threshold. On the basis of our theoretical estimates, we assign a peak in the high-energy portion of the spectra as due to deexcitation of triply excited $\mathrm{LiI}2{s}^{2}2p$ and $2s2{p}^{2}$ configurations.