Doubly Excited Feshbach States ofCl−

An investigation of doubly excited states of the negative chlorine ion using the method of configuration interaction has located several Feshbach autodetaching resonances in the energy region 8.5-12.6 eV. Dominant two-particle excitations considered include $3p^2\to 4s^2$, $4s4p$, $4p^2$, and $5s^2$. The results obtained are useful in interpreting the recent experimental structure observed in the electron spectrum resulting from collisions of ground-state ${\mathrm{Cl}}^{-}$ ions with helium- and hydrogen-gas targets.