The single- and double-electron detachment processes have been studied for 85 keV ${\mathrm{H}}^{\mathrm{-}}$ on He collisions measuring the energy spectra of the electrons emitted in forward direction. In the spectrum belonging to the single-electron loss (SEL) the nonresonant part (cusp) has been resolved from the resonant part [lines from the (2s2p${)}^1$${\mathit{P}}^{\mathit{o}}$ shape resonance of ${\mathrm{H}}^{\mathrm{-}}$]. The ratio of the integrated yield of the double-electron loss (DEL) to that of SEL was found to be 0.36±0.02. The yield of the cusp in the SEL spectrum was found to be surprisingly small, only (70±20)% of the yield of the cusp in the DEL spectrum. The formation of the cusp in SEL is interpreted as a result of dipolar interaction between the electron and the outgoing ${\mathrm{H}}^0$ atom. © 1996 The American Physical Society.

• Received 25 March 1996

DOI:https://doi.org/10.1103/PhysRevA.54.2161