Equilibrium charge-state fractions of ${\mathrm{Li}}^{\mathrm{-}}$, ${\mathrm{Li}}^0$, and ${\mathrm{Li}}^{+}$ in Mg, Sr, and Cs vapors

${\mathrm{Li}}^{+}$ ions, accelerated to energies between 1 and 20 keV, pass through thick vapor targets of Mg, Sr, and Cs. The ions that emerge into a narrow, forward-directed cone are electrostatically separated into three charge-state components: ${\mathrm{Li}}^{\mathrm{-}}$, ${\mathrm{Li}}^0$, and ${\mathrm{Li}}^{+}$. The principal results over this energy range are the following: (1) The negative fraction peaks at 5% near 5 keV for a Cs target, and is less than 1% in Mg and Sr targets; (2) for Sr and Cs targets, the beam is greater than 90% neutral; and (3) for a Mg target, the beam does not neutralize at the lowest energies studied, remaining mostly positive between 1 and 10 keV.