The zero-core-contribution model allows photodetachment cross sections to be computed using a few readily accessible input parameters. We apply this model to the computation of photodetachment cross sections for the homonuclear diatomic ions ${\mathrm{O}}_2^{-}$ and ${\mathrm{S}}_2^{-}$, which have ${\pi }_g$ outer orbitals. Values are calculated for the total cross sections, partial cross sections for each vibrational channel, and angular distributions for each vibrational channel. The results are in good agreement with experimental values. Inclusion of vibrational effects allows the prediction of total photodetachment cross sections as a function of ion vibrational temperature. This allows comparison with both swarm and beam-type experiments. The simplicity of the model makes it of use in the interpretation of experimental results. This is illustrated by applying the model to infer equilibrium internuclear distances. We obtain $r_e^{\prime \prime }=1.348\mathrm{}$ Å for ${\mathrm{O}}_2^{-}$ and $r_e^{\prime \prime }=2.004\mathrm{}$ Å for ${\mathrm{S}}_2^{-}$. We anticipate that the simplicity of the model will allow its application to heteronuclear diatomic and polyatomic negative ions.

• Received 23 December 1980

DOI:https://doi.org/10.1103/PhysRevA.23.2866