Electron-impact detachment fromB−

Cross sections for electron-impact single and double detachment from $B^{-}$ have been measured from 0 to 200 eV. The single-detachment cross section peaks at 4–5 eV with a cross-section maximum of about ${10}^{-14}{\mathrm{cm}}^2$. A ${(2p}^3)$ ${}^{4}S$ state has recently been predicted to give rise to a resonance state in the $H^{2-}$ dianion [T. Sommerfeld et al., Phys. Rev. A 55 1903 (1997)]. We observe no resonances in the detachment cross section of $B^{-}$ and hence no sign of an equivalent shortlived $B^{2-}{(2p}^3)$ state. The ratio of the double- to single-detachment cross section reaches a constant value of 3% at energies above 50 eV. A simple model relates this number to a shake-off probability of about 90%. The ratio between double and single ionization of neutral atomic targets at high energy is also discussed, and the model relates this ratio to the shake-off probability in the sudden approximation.