Resolving a discrepancy between experimental and theoretical lifetimes in atomic negative ions

A recent measurement of the lifetime of the excited 3p⁵ state in the S^- negative ion, which is dominated by a forbidden magnetic dipole transition to the ² P_{3/ 2} ground state, reveals a discrepancy with earlier theoretical predictions. To investigate this we have performed systematic and large-scale multiconfiguration Dirac-Hartree-Fock calculations for this system. After including a careful treatment of correlation and relativistic effects, we predict a well-converged value for this lifetime, with an uncertainty considerably less than 1%, thereby removing the apparent conflict between theory and experiment. We also show that this result corresponds to the non-relativistic limit in the LS coupling approximation for the magnetic dipole transition within this ² P term. In addition we demonstrate the usefulness of the latter approach for ² P transitions in O^-, Se^- and Te^-, as well as for analogous M1 transitions within ² D terms in Ni^- and Pt^- ions.