Photodetachment from negative ions in a static electric field has been studied using ${\mathrm{Cl}}^{\mathrm{-}}$ and ${\mathrm{S}}^{\mathrm{-}}$. These experiments were done with greater precision than previous studies and allow a quantitative comparison of data with theory. A 10-keV ion beam was sent through a region with fields of up to 1.5 kV/cm applied parallel to the beam velocity. A pulsed dye-laser beam, perpendicular to the ion beam, photoneutralized the ions. The relative cross sections were measured by detecting the resulting fast neutral atoms. Detachment below threshold and oscillations on the cross section above threshold were observed near the ${\mathrm{S}}^{\mathrm{-}}$ threshold at 16 269.5 ${\mathrm{cm}}^{\mathrm{-}1}$ and near the ${\mathrm{Cl}}^{\mathrm{-}}$ threshold at 29 138.3 ${\mathrm{cm}}^{\mathrm{-}1}$. The phase of the oscillations in the data is in good agreement with predictions for s-wave photodetachment in a static electric field, but the amplitude of the oscillations is found to be slightly reduced.

• Received 20 August 1992

DOI:https://doi.org/10.1103/PhysRevA.47.1946