Abstract
The theory of the photodetachment of negative ions in an external static electric field developed earlier is applied to photodetachment of the sulphur and chlorine negative ions. The photodetachment cross section in the presence of the electric field is modified by a modulation factor which is calculated including the rescattering effect, i.e. the scattering of the electron wave reflected by the electric field's potential barrier. The modulation factor is expressed in terms of the scattering lengths for electron-neutral-atom scattering. The scattering lengths are calculated by the method of extrapolation of potential parameters along isoelectronic series of positive ions and corresponding neutral atoms. The low-energy electron scattering cross sections for the S and Cl atoms are obtained, and the Ramsauer effect for these atoms is studied. The rescattering effect in the photodetachment cross sections is small, and cannot explain the observed reduction of the oscillations in the modulation factor.

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