ELECTRON-IMPACT DETACHMENT FROM B-

Cross sections for electron-impact single and double detachment from B - have been measured from 0 to 200 eV. The single-detachment cross sec tion peaks at 4-5 eV with a cross-section maximum of about 10(-14) cm( 2). A (2p(3)) S-4 state has recently been predicted to give rise to a resonance state in the H2- dianion [T. Sommerfeld et al., Phys. Rev. A 55 1903 (1997)]. We observe no resonances in the detachment cross sec tion of B- and hence no sign of an equivalent shortlived B2-(2p(3)) st ate. The ratio of the double- to single-detachment cross section reach es a constant value of 3% at energies above 50 eV. A simple model rela tes this number to a shake-off probability of about 90%. The ratio bet ween double and single ionization of neutral atomic targets at high en ergy is also discussed, and the model relates this ratio to the shake- off probability in the sudden approximation. [S1050-2947(98)09709-1].